UNIVERSITYo/tALIFORNIA 
COLLEGE  of  MINING 

DEPARTMENTAL 
LIBRARY 

*  *  • 
BEQUEST  OF 


SAMUELBENEDICTCHRISTY 

PROFESSOR  OF 

MINING  AND   METALLURGY 
1885-1914 


CYANIDE  PROCESSES. 


BY 

E.  B.  WILSON,  E.M. 
it 


FIRST   EDITION. 

FIRST   THOUSAND. 


NEW  YORK: 

JOHN    WILEY    &    SONS. 

LONDON-   CHAPMAN  &  HALL,  LIMITED. 

1896. 


Copyright,  1895, 

BY 

E.  B    WILSON. 


BRAUNWORTH,    MUNN    A    BARBER,    PRINTERS   AND    BOOKBINDERS,    NEW   YORK. 


CONTENTS. 


PAGE 

INTRODUCTION iii 

CHAPTER  I.  STAMP-MILL  WORK i 

II.  AMALGAMATION 7 

III.  FOUNDATION  OF  CYANIDE  PROCESS 10 

IV.  CHEMISTRY  OF  THE  OPERATION 21 

V.  LEACHING  THE  ORE 29 

VI.  ZINC  AS  A  PRECIPITANT , 38 

VII.  TREATMENT  OF  BULLION 43 

VIII.  THE  RECOVERY  BY  THE  CYANIDE  PROCESS 48 

IX.  LABORATORY  WORK 54 

X.  GOLD    AND    SILVER    SOLVENTS    COMBINED    WITH 

ELECTRICAL  ACTION 72 

XI.  CYANIDE  SOLUTION  WITH  VARIOUS  ELECTRODES  ...  80 

XII.  THE  CURRENT 87 

XIII.  ANODES 92 

XIV.  CATHODES 97 

XV.  VARIOUS  PROCESSES  AND  CONCLUSIONS  , 103 

AUTHORITIES in 

USEFUL  INFORMATION. 113 


INTRODUCTION. 


THE  author's  investigations  of  the  Cyanide  Process 
were  first  confined  to  Patent  Office  literature,  together 
with  such  extracts  as  appeared  from  time  to  time  in 
technical  journals  and  society  periodicals.  For  his  own 
benefit  he  grouped  the  numerous  articles  which  gave 
but  a  passing  insight  into  the  subject.  His  investiga- 
tions upon  the  subject  made  to  verify  the  results  as 
set  forth  by  the  various  writers  convinced  him  that  by 
grouping  the  items  of  importance  in  connection  with 
the  subject  considerable  light  could  be  thrown  on  the 
process  and  much  time  saved. 

This  grouping  may  also  have  the  effect  of  bringing 
out  new  ideas  upon  the  subject,  and  the  one  point 
mastered  will  not  be  forgotten  while  examining  the 
next  article  on  the  subject.  The  writer  is  indebted 
to  many  for  the  ideas  here  advanced,  and  takes  this 
occasion  to  express  his  gratitude  to  them  for  their 
valuable  contributions.  He  has  not  attempted  to  go 
into  the  mechanical  arrangements  for  the  process,  be- 
cause on  the  one  hand  circumstances  will  vary  at  each 
plant,  and  on  the  other  the  arrangement  of  details 
belongs  to  the  engineer  of  the  company  controlling 
and  promoting  the  patents.  The  author's  object  has 


in 


IV  INTRODUCTION. 

been  to  confine  the  text  to  the  process  itself  and  such 
points  as  have  special  bearing  on  its  success.  While 
the  rudiments  of  this  method  were  known  as  early  as 
1806,  it  is  only  within  the  past  few  years  that  its 
practical  value  has  been  acknowledged,  and  even  at 
the  present  time  many  prefer  to  use  more  complicated 
processes  rather  than  change  from  a  plan  they  are 
familiar  with  to  one  which  is  comparatively  unfamiliar. 

The  writer  has  endeavored  to  be  unbiassed  in  his 
remarks,  but  after  reading  and  rereading  some  thirty 
different  patent  specifications  with  their  claims,  he 
fears  stress  enough  has  not  been  laid  on  defective 
points,  and  begs  the  reader's  consideration  if  his 
opinions  as  set  forth  favor  any  one  patentee  more 
than  another. 

What  he  desires  to  bring  out  clearly  are  the  points 
which  he  considers  of  value  as  he  sees  them,  and  to 
avoid  those  whose  value  was  yet  to  be  demonstrated. 
An  examination  of  these  numerous  patents  leads  him 
to  the  conclusion  long  ago  reached  by  some  eminent 
authority  that  "  there  is  nothing  new  under  the  sun." 

For  the  benefit  of  those  interested  in  mines  he  has 
dilated  somewhat  on  stamp-mill  work ;  for  the  benefit 
of  the  miner  he  has  made  remarks  which  he  hopes 
will  be  of  value;  and  lastly,  for  the  mining  engineer 
he  has  told  all  he  knows  of  the  subject  at  the  present 
time. 

THE  AUTHOR. 


CYANIDE    PROCESSES. 


CHAPTER  I. 

PRACTICALLY  speaking,  there  are  but  two  classes 
of  ores  which  contain  the  precious  metals :  free-mill- 
ing, or  those  which  deliver  up  their  gold  contents  to 
amalgamation,  and  refractory,  which  only  do  so  in  a 
measure  or  not  at  all. 

The  term  "  free-milling  "  is  derived  from  the  gold 
in  the  ores  being  in  such  a  state  that  upon  being 
crushed  in  a  stamp-mill  the  particles  of  gold  sepa- 
rate from  the  rock,  free,  to  be  then  brought  into  con- 
tact with  mercury,  and  from  which  they  can  only  be 
freed  by  distillation.  This  treatment  is  termed  arnal- 
gamation. 

The  term  "  refractory  ores'*  is  derived  from  the 
fact  that  all  gold-bearing  ores  are  not  "  free-milling," 
and  will  not  amalgamate  their  gold  with  mercury ;  in 
other  words,  obstinately  refuse  to  yield  up  their  gold 
to  the  easiest  method  of  recovery. 

Free-milling  ores  do  not  yield  all  their  gold,  and 
refractory  ores  will  at  times  yield  some  of  their  gold 
to  mercury,  but  the  circumstances  connected  with 


2  CYANIDE  PROCESSES. 

such  results  will  not  change  the  names  adopted,  as 
will  be  shown.  As  we  are  dealing  with  ores  with  ref- 
erence to  their  adaptability  to  the  cyanide  treatment, 
and  since  all  ores  so  treated  must  be  stamped  or 
crushed  for  this  treatment,  we  will  consider  that  a  sur- 
vey of  stamp-mill  work  should  precede  the  details  of 
the  process. 

In  all  work  uniformity  of  product  is  desirable,  but 
particularly  is  this  the  case  in  metallurgical  work,  to 
obtain  the  most  satisfactory  results.  Of  the  two 
methods  of  crushing  or  stamping  in  use,  namely,  the 
wet  and  the  dry,  the  wet  has  given  the  better  results 
both  as  to  uniformity  of  the  grains  and  speed  of 
crushing. 

When  wet  crushing  is  practised,  water  is  allowed  to 
flow  into  the  mortar  of  the  stamp-mill  and  flow  out 
through  a  screen ;  sometimes  two  screens  are  used, 
one  on  each  side  of  the  mortar,  giving  a  double  dis- 
charge. The  sized  mesh  used  on  these  screens  varies 
from  sixty  to  one  hundred  for  amalgamation,  but  for 
the  cyanide  process  it  has  been  in  many  instances 
possible  to  use  3O-mesh  screens  and  even  very  much 
coarser. 

The  size  of  the  mesh  of  the  screen  determines  the 
degree  of  fineness  to  which  crushing  is  to  be  carried, 
as  all  fine  particles  which  can  pass  the  mesh  are  carried 
through  by  water,  while  all  that  cannot  pass  through 
remain  in  the  mortar  to  be  pounded  until  they  can. 


CYANIDE  PROCESSES.  3 

With  dry  crushing  two  discharge-screens  can  be  em- 
ployed to  give  more  uniform  results  and  faster  pulver- 
ization. 

When  crushing  dry,  the  stamps  falling  on  the  ore 
pulverizes  it ;  there  being  no  water  to  move  it  away, 
the  dry  powder  accumulates  in  the  battery  mortar 
and  under  the  stamps,  thus  retarding  the  process  and 
very  often  forming  a  cushion  for  the  stamp,  not  al- 
lowing it  to  crush  particles  uniformly. 

The  various  machines  so  far  invented  have  not 
proved  satisfactory  for  dry  crushing ;  and  while  with 
new  rolls  a  very  uniform  product  can  be  obtained, 
it  is  an  endless  repetition  of  screening  and  returning 
to  the  rolls  again. 

The  best  dry  crushing  so  far  witnessed  by  the 
writer  is  accomplished  by  Krupp's  pulverizer;  but 
even  this  is  very  slow,  still  there  is  no  elevating  and 
screening. 

This  field  for  inventive  genius  is  open.  There  is 
needed  very  badly  a  good  dry  crusher  which  will 
crush  uniformly,  speedily,  not  clog  with  damp  ores, 
not  break  with  hard  ores,  will  crush  both  hard  and 
soft  rock  equally  well,  will  not  round  the  particles, 
but  leave  rough  surfaces  as  do  stamps,  and  will  not 
be  too  costly  for  repairs.  Any  machine  that  can  take 
up  and  meet  all  these  requirements  will  take  the  place 
of  stamp-mills.  One  of  the  obstacles  to  be  overcome 
in  crushing  wet  for  the  cyanide  process  is  the  amount 


4  CYANIDE  PROCESSES. 

of  water  used  necessary  to  do  the  work  of  uniform 
crushing.  This  water  has  been  in  some  instances  re- 
turned from  settling-tanks  back  into  the  mortar  to  be 
used  again  and  again.  While  there  are  no  objections 
to  the  use  of  this  water,  there  are  to  pumping 
it.  It  is  understood  that  with  wet  crushing  water 
enough  must  be  used  to  allow  the  sludge  to  flow 
through  the  screens.  It  is  often  to  the  advantage  of 
the  cyanide  process  that  coarse  crushing  is  allowable, 
both  as  to  amount  of  water  used  and  time  saved  in 
crushing;  still  even  this  advantage  of  time  is  more 
than  counterbalanced  by  time  lost  in  treatment  of  ore 
by  the  cyanide  solution  when  coarse  crushing  is  prac- 
tised. For  if  we  are  able  to  save  time  in  crushing,  and 
subsequent  drainage  of  water  and  liquor,  we  must 
allow  the  cyanide  solution  to  remain  longer  in  contact 
with  ore  being  treated. 

On  the  other  hand,  when  fine  crushing  is  employed, 
as  it  must  be  at  times,  the  water  drains  slowly  from 
the  settling-tanks,  leaving  the  fine  ore  very  firmly 
packed,  and  sometimes  so  firmly  packed,  if  clayey  or 
slimy,  as  to  almost  allow  of  no  filtration,  even  when 
suction  and  other  devices  are  employed  to  assist 
gravity.  The  average  speed  of  drainage  is  about  12 
inches  per  hour,  which  can  be  increased  mechanically ; 
but  even  in  this  case  we  shall  still  have  the  packing  to 
contend  with,  which  will  interfere  with  cyanide  leach- 
ings. 


CYANIDE  PROCESSES.  5 

The  character  of  the  ore  will  determine  the  degree 
of  fineness  in  crushing. 

An  open  porous  ore  might  be  crushed  to  the  size  of 
a  pea,  while  a  compact  ore  with  metal  disseminated 
through  it  in  grains  may  need  6o-mesh  or  finer. 

If  the  metal  is  in  porous  or  loose  ore  in  form  of 
seams  or  streaks,  coarse  crushing  will  answer. 

It  is  often  necessary  with  refractory  ores  to  use  a 
preliminary  treatment  of  lime  to  neutralize  the 
acids  which  usually  are  found  in  partially  oxidized 
sulphur  pyritous  ores,  and  are  more  or  less  dissoluble 
in  water.  Attempts  have  been  made  to  neutralize 
these  ores  in  the  process  of  stamping  by  adding 
lime  to  the  stamp-water.  The  objection  to  this  pro- 
ceeding is  that  a  great  degree  of  uncertainty  must 
prevail  as  to  the  amount  of  lime  required ;  and  more- 
over, as  the  lime  must  be  leached  out  of  the  ore  by 
water  later  on,  not  much  is  to  be  gained,  but  consider- 
able annoyance  will  be  caused  if  too  much  lime  finds 
its  way  into  the  ore. 

Mr.  A.  B.  Paul  used  a  cyanide  solution  in  the  stamp- 
battery,  the  object  being  to  take  up  gold  as  it  was 
liberated  from  the  ore,  thus  hastening  the  operation 
and  lessening  the  amount  of  water  waste. 

There  are  several  objections  to  this  practice  which 
make  it  unadvisable,  and  which  summed  up  are : 

That  loss  of  cyanide  takes  place  ;  no  coarse  gold  can 


O  CYANIDE  PROCESSES. 

be  taken  up ;   and  that   its  action  is  of  no  great  as- 
sistance to  the  mercury  to  be  used  in  such  instances. 

Also  the  amount  of  gold  recovered  by  this  method 
would  be  so  small  that  the  customary  leaching  must 
follow;  hence  no  time  is  gained.  Again,  this  system 
would  not  be  feasible  if  sulphurets  were  being  treated. 

The  resume  of  stamp-mill  work  for  our  investiga- 
tions amounts  to  this : 

That  the  more  uniform  the  particles  are  crushed 
the  more  complete  will  be  the  extraction  results  with 
cyanide ; 

That  the  degree  of  fineness  required  will  depend 
upon  the  character  of  the  ore  and  the  method  of  the 
distribution  of  metal  in  the  ore ; 

That  porous  ores  require  less  fineness  than  compact 
ores; 

That  dry, crushing  does  not  give  as  uniform  particles 
as  wet  crushing ; 

That  the  use  of  lime  or  cyanide  solution  in  the  bat- 
teries is  not  to  be  commended ; 

That  where  particles  of  free  gold  exist  in  any 
appreciable  size  mercury  can  be  used  in  the  stamp- 
mortar  to  facilitate  recovery  when  sulphides  are  not 
being  stamped. 


CHAPTER  II. 

AMALGAMATION. 

REFRACTORY  ORES — TAILINGS  AND  CONCENTRATES. 

UNDER  the  heading  of  refractory  ores  come  those 
parts  of  free-milling  ores  which  cannot  be  delivered 
of  their  gold  by  mercury.  With  good  stamp-mill 
practice,  there  will  float  away  in  the  slimes  or  tailings 
a  percentage  of  gold  if  wet  stamping  is  followed, 
and  the  same  percentage  of  loss  occurs  when  dry 
crushing  is  practised.  The  cause  of  this  loss  will 
be  stated  later  on.  Ores  containing  the  precious 
metals,  free-milling  at  the  surface  very  often  become 
refractory  when  they  reach  a  depth  where  the  elements 
cannot  obtain  access  to  them ;  this  depth  is  usually 
water-level.  The  cyanide  process  is  particularly 
adapted  to  this  class  of  ores. 

To  obtain  the  gold  from  free-milling  ores  mercury 
is  placed  in  the  mortar  of  the  stamp-mill  batteries, 
and  amalgamated  copper  plates  placed  so  that  the  gold 
going  over  them  with  slimes  may  be  captured  by  the 
mercury  on  the  plates.  This  amalgamation,  as  it  is 
called,  will  recover  by  good  mill-work  60$  of  the  gold 
in  the  ore. 

7 


8  CYANIDE  PROCESSES. 

The  various  reasons  advanced  why  more  gold  is  not 
recovered  are  that  the  particles  are  too  fine,  and  that 
others  are  covered  with  a  film  of  oxide,  sulphide,  or 
tarnish  which  prevents  the  mercury  from  coming  in 
contact  with  the  gold,  thus  preventing  its  uniting  with 
it.  These  fine  particles  and  tarnished  gold  are  virtu- 
ally then  refractory.  After  they  have  left  the  stamps 
they  are  termed  tailings.  It  has  been  customary  to 
grind  these  tailings  in  a  pan  with  mercury,  or  to  con- 
centrate them  by  vanners,  bumping-tables,  or  other 
means.  The  cyanide  process  acts  very  readily  and 
completely  on  most  tailings,  so  that  its  introduction 
has  been  the  means  of  recovering  immense  quantities 
of  gold  from  tailings. 

Those  ores  which  carry  sulphides,  tellurides,  ar- 
senides, antimonides,  and  base-metal  compounds  are 
refractory.  When  containing  considerable  gold,  if 
treated  with  mercury,  they  make  the  mercury  "flour," 
or  else  sicken,  so  that  both  mercury  and  gold  are  lost. 

Sickened  mercury  becomes  so  sluggish  by  admix- 
ture of  base  metals  that  it  will  not  act  upon  gold. 
This  mercury  can  be  restored  to  its  normal  condition 
so  that  it  is  not  a  loss,  but  while  it  is  sickened  it  is  of 
no  practical  value  for  gold  recovery. 

Flouring  of  mercury  is  a  much  more  serious  affair. 
It  is  due  to  sulphides  coating  the  mercury  and  prevent- 
ing the  globules  of  mercury  from  uniting  when  once 
separated.  Continued  working  subdivides  the  mercury 


CYANIDE  PROCESSES.  9 

more  and  more  until  it  becomes  a  black  slimy  mass 
which  will  be  found  difficult  to  settle  in  water,  and 
is  carried  off  in  the  washings  and  lost. 

The  separation  of  this  metallic  slime  from  the 
heavier  portions  of  the  ore  is  almost  an  impossibility. 

Various  schemes  have  been  proposed  and  various 
chemicals  tried  to  obviate  the  difficulties  encountered 
by  flouring  and  sickening  of  the  mercury,  but  we  have 
heard  of  none  which  have  proved  entirely  satisfactory 
to  other  than  the  inventor. 

When  fine  or  tarnished  gold  particles  are  met  with, 
and  the  mercury  retains  its  bright  appearance  and 
fluidity,  amalgamation  does  not  always '  take  place. 
To  force  the  gold  to  meet  the  mercury  mechanical 
means,  such  as  grinding  with  mercury,  has  been  resorted 
to.  If  sulphides  are  present,  this  will  cause  the  mer- 
cury to  flour;  if  base  metals  are  present,  sickening  of 
the  amalgam  will  result.  The  proper  method  for 
treating  such  ores  before  the  introduction  of  the  cya- 
nide process  was  concentration,  or  assortment  for  the 
smelters.  As  we  are  dealing  merely  with  stamp-mill 
work  only  as  it  effects  the  cyanide  process,  we  refer 
those  who  desire  further  information  to  Prof.  T.  A. 
Rickards'  articles  in  the  Engineering  and  Mining  Jour- 
nal,  also  to  "California  Gold  Mill  Practices"  by  Ed.  B. 
Preston,  which  are  the  most  replete  with  information 
of  any  in  our  language,  at  least  that  we  have  observed. 


CHAPTER  III. 

FOUNDATION  OF  CYANIDE  PROCESS. 

THAT  gold  was  soluble  in  cyanide  of  potassium  solu- 
tions was  known  to  Hagen  in  1806.  L.  Eisner  stated 
in  1844  that  gold  and  silver  could  be  dissolved  in 
potassium  cyanide  without  decomposition  of  water. 
He  further  stated  that  the  dissolution  of  the  metals  is 
the  consequence  of  the  action  of  oxygen,  which,  ab- 
sorbed from  the  air,  decomposed  part  of  the  cyanides, 
thus  forming  a  double  salt  auro-potassic  cyanide, 
which  has  later  been  stated  in  the  following  equation, 
known  as  "  Eisner's  Equation": 

2Au  +  4KCy  +  O  +  H30  =  2AuKCy2  +  2KOH. 

The  first  scientific  literature  on  the  subject  is  by 
Prince  Bagration  in  1843.  He  concluded  his  paper 
with  the  remark  that  in  the  future  cyanide  of  potas- 
sium must  be  enumerated  among  the  solvents  of  gold. 
Faraday  made  use  of  a  cyanide  solution  to  produce 
thin  films  of  gold  in  1857.  Ten  years  later  J.  H. 
Rae  took  out  the  first  patent  for  applying  cyanide  to 
obtain  gold  from  the  ores  direct.  He  was  followed 
by  Faucett  in  1881  ;  He  in  turn  by  Sanders  in  1881 ; 

10 


CYANIDE   PROCESSES.  II 

then  by  J.  W.  Simpson  in  1885  ;  finally  by  MacArthur 
and  Forrest  in  1889.  To  these  latter  men  is  due  the 
praise,  not  that  they  were  the  first  discoverers,  but 
because  they  pushed  their  inventions,  and  enabled  the 
recovery  of  $14,000,000  in  five  years  by  their  process 
which  otherwise  would  be  irrecoverably  lost. 

It  is  of  no  special  moment  to  us  who  discovered  the 
process  or  whose  process  or  patent  is  valid :  that 
MacArthur  people  proved  the  way  by  practical  demon- 
stration is  of  more  value  to  the  world  than  who  owns 
the  patent.  After  the  examination  of  some  thirty  or 
forty  patent  claims  it  appears  to  the  writer  that  the 
patent  offices  are  more  at  fault  in  granting  claims  than 
those  who  make  the  claims  and  obtain  the  patents. 

Eisner's  equation  has  caused  such  comment  as  to 
have  led  some  to  jump  at  conclusions  too  hastily. 
Even  MacArthur  stated  that  oxygen  in  the  solution 
was  not  necessary  for  the  dissolution  of  gold,  but  we 
believe  he  has  repented.  A  pure  solution  of  potas- 
sium cyanide  will  not  dissolve  gold  to  any  great  extent 
when  immersed  in  it,  but  dissolves  it  readily  when 
oxygen  is  present. 

For  example,  if  gold-leaf  is  placed  on  the  surface  of 
a  cyanide  solution,  it  will  dissolve  in  a  few  minutes, 
and  the  stronger  the  solution  the  quicker  it  will  dis- 
solve ;  however,  if  submerged  in  the  solution  it  dis- 
solves but  slowly,  the  strength  of  the  solution  effect- 
ing its  rate  of  dissolution  but  slightly. 


12  CYANIDE   PROCESSES. 

MacLaurin  of  New  Zealand  made  some  experi- 
ments which  we  quote  from. 

He  used  gold-leaf  of  uniform  thickness,  and  his  de- 
ductions were  that  oxygen  was  necessary  for  the  solu- 
tion of  cyanide  if  it  was  to  dissolve  gold  with  any 
rapidity.  A  piece  of  gold-leaf  placed  in  a  stoppered 
bottle  lost  o.i  8$  of  its  weight  in  ninety-two  hours. 

Another  piece  placed  in  open  bottle  lost  9.1$  of  its 
weight  in  sixty-two  hours.  Still  another  piece  placed 
in  a  bottle  with  oxygen  lost  24.2$  of  its  weight  in 
ninety-six  hours.  The  strength  of  the  solutions  was 
identical  in  every  instance. 

Experiments  were  made  by  the  State  Mining  Bureau 
of  California  with  dilute  cyanide  solution  upon  metal- 
lic gold. 

With  a  i  per  cent  solution  it  was  found  possible 
to  dissolve  such  gold-leaf  as  is  used  by  sign-painters 
in  one  hour.  When  dentists'  foil  was  used,  about  six 
times  thicker  than  painters'  foil,  it  required  forty- 
eight  hours  to  dissolve. 

Mr.  J.  B.  Hanney  verified  Eisner's  equation  and 
MacLaurin's  experiments  in  a  practical  way.  His 
theory  was  that  dilute  cyanide  solutions  acted  more 
rapidly  on  gold.  He  attributed  this  to  the  cyanide 
displacing  oxygen  by  dissolving  in  the  water,  and  that 
therefore  gold  could  not  dissolve  until  oxygen  had  been 
absorbed  from  the  air.  To  carry  out  this  theory  he 
treated  ores  with  dilute  and  then  with  strong  solution. 


CYANIDE   PROCESSES.  13 

He  found  that  the  rate  of  dissolution  of  gold  in- 
creased with  the  strength  of  the  solution,  provided 
oxygen  of  the  air  could  come  in  contact  with  the  gold. 

Mr.  Hanney  invented  an  electro-chemical  apparatus 
which  he  used  in  his  experiments.  In  direct  oppo- 
sition to  this  Mr.  Miller  has  patented  an  apparatus 
to  keep  the  air  away  from  the  solution. 

From  MacLaurin's  experiments  we  deduce: 

1 .  That   oxygen  is  necessary  for  dissolving  gold  in 
a   cyanide  solution,   and    that    it    combines   with  the 
potassium  of  the  potassium  cyanide  in  the  proportion 
required  by  Eisner's  equation. 

2.  The  rate  at  which  gold  is  dissolved  in  a  solution 
of  potassium  cyanide  passes  through  its  maximum  in 
passing  from  dilute  to  concentrated  solution,   due  to 
the   fact  that  the   solubility   of  oxygen  in  a  cyanide 
solution  decreases  with  the  concentration.     (See  "  Gen- 
eral Information.") 

The  MacArthur-Forrest  patent,  May  14,  1889,  con- 
sisted in  subjecting  the  ores  to  a  small  quantity  of 
cyanide  solution  without  any  other  chemically  active 
agent,  but  they  state  the  process  may  be  expedited 
by  stirring. 

Mr.  J.  C.  Montgomerie  added  NaHO,  then  NaO2, 
finally  Na2O2,  each  oxide  being  the  cause  of  a  separate 
patent,  and,  as  he  says,  giving  equally  good  results. 

Carl  Moldenhauer  claims  that  in  order  to  extract 
gold  it  is  necessary  to  simultaneously  oxidize  the  solu- 


14  CYANIDE   PROCESSES. 

tion.  Instead  of  depending  upon  air  and  agitation 
he  dissolves  gold  with  cyanide  of  potassium  in  the 
presence  of  permanganate  of  potash.  Later  on  he  used 
ferricyanide  of  potassium  in  connection  with  cyanide 
of  potassium  to  make  the  action  more  energetic,  but 
states  that  ferricyanide  of  potassium  will  not  dissolve 
gold. 

THE    SOLUTION. 

The  acknowledged  practice  for  economical  results 
is  to  use  a  weak  solution  of  potassium  cyanide.  Mac- 
Arthur  says  regulate  the  quantity  of  cyanide  so  that 
its  cyanogen  will  be  in  proportion  to  the  gold  and 
silver  in  the  ore-charge,  but  in  all  cases  to  use  suffi- 
cient water  to  keep  the  solution  extremely  dilute,  be- 
cause when  dilute  its  preference  is  for  gold  and  silver 
rather  than  the  baser  metals. 

"We  find  it  most  advantageous  to  use  a  quantity 
of  cyanide  the  cyanogen  of  which  is  equal  in  weight 
to  from  one  to  four  parts  for  every  thousand  parts  of 
ore,  and  we  dissolve  the  cyanide  in  a  quantity  of 
water  of  about  half  the  weight  of  the  ore." 

In  other  words,  the  solution  should  contain  8  parts 
of  cyanogen  to  1000  parts  of  water  by  weight.  This 
proportion  would  give  20  pounds  KCy  to  the  1000 
pounds  water,  or  40  pounds  to  the  ton  of  ore.  This 
amount  is  not  sufficient,  except  for  the  weak  solution, 
at  the  commencement  of  the  operation.  The  action 


CYANIDE   PROCESSES.  I  5 

of  cyanide  upon  gold  is  slow  at  first,  but  increases 
with  time  ;  hence  by  using  a  weak  solution  first  to  com- 
mence the  operation  the  way  is  paved  for  the  standard 
or  strong  solution,  and  at  the  same  time  the  chances 
are  lessened  for  the  strong  solution  attacking  the  base 
metals  present.  There  seems  to  be  no  definite  rule 
regarding  the  amount  of  cyanide  required  for  taking  up 
one  ounce  of  gold.  Eisner's  equation  theoretically 
gives  the  amount  as  I  part  cyanogen  for  every  1.5 
parts  of  gold  to  be  dissolved.  Practical  results  require 
40  parts  cyanogen  to  I  part  of  gold,  and  from  this 
down  according  to  the  care  used  and  safeguards  em- 
ployed to  economize  its  use. 

Good  results  have  been  obtained  with  0.05  per  cent 
of  cyanogen  in  the  solution  to  the  ton  of  ore. 

The  percentage  of  cyanide  required  will  depend 
upon  the  nature  of  the  ore  and  the  methods  used. 

Losses  must  surely  occur  in  treating  ores  contain- 
ing acids  or  not  thoroughly  oxidized  from  acid  salts. 

They  will  also  occur  by  Eisner's  rule ;  again,  by 
absorption  of  the  vats ;  by  coming  in  contact  with 
carbonic  acid  ;  they  will  also  occur  in  the  zinc  pre- 
cipitation-boxes. 

There  may  also  some  loss  occur  by  coming  in  con- 
tact with  iron 

Mr.  Paul  says  the  proper  per  cent  of  the  solution 
should  be  as  testing  will  show,  viz.,  the  proper  per 
cent  for  extracting  the  highest  per  cent  of  the  pre- 


l6  CYANIDE  PROCESSES. 

cious  metals,  "say  from  one  half  per  cent  to  one  and 
one  half  per  cent,  then  treating  the  ore  for  a  given 
length  of  time  with  this  solution." 

Mr.  Paul's  rule  is  about  the  only  rule  we  have  to  go 
by,  and  it  must  be  the  case  from  the  nature  of 
ores  differing  so  widely  in  character. 

Time  is  more  an  element  for  the  successful  opera- 
tion of  this  process  than  a  high  percentage  of  cyano- 
gen. As  this  depends  upon  the  character  of  the  ore, 
tests  must  be  employed,  as  illustrated  under  head- 
ing of  "  Laboratory- work." 

The  action  of  the  solution  is  to  penetrate  the  ore, 
find  the  gold,  and  bring  it  out ;  if,  therefore,  coarse 
crushing  can  be  used,  time  may  be  gained  in  crushing 
and  rapidity  of  leaching,  which  will  compensate  for 
the  extra  time  required  for  keeping  the  solution  in 
contact  with  the  ore. 

Time  may  be  saved  by  agitating  the  ore  with  the 
solution,  either  by  mechanical  stirrers  or  rotating 
barrels.  These  agitators  are  especially  valuable  for 
quick  work  where  fine  crushing  is  necessary  or  clayey 
slimes  and  tailings  are  to  be  dealt  with.  To  facilitate 
matters  filter-presses  and  mechanical  suction  of  the 
liquid  from  the  vats  can  be  employed.  In  South 
Africa  the  vats  and  charges  are  so  huge  that  mechan- 
ical stirrers  would  require  considerable  power,  and  as 
the  vats  stand  by  themselves,  requiring  no  watching, 
no  power  is  considered  necessary.  In  other  words,  to 


CYANIDE   PROCESSES.  !/ 

avoid  the  use  of  power  they  increase  the  size  of  the 
vats,  saving  time  by  the  great  charges  treated. 

Slimes  or  tailings  from  other  processes  can  be 
readily  treated  by  the  cyanide  method ;  in  fact  this 
makes  it  the  most  important  all-around  metallurgical 
factor  yet  put  in  practice,  its  use  not  being  limited  to 
free-milling  or  yet  refractory  ores,  but  adaptable  to 
many  and  various  phases  of  gold  extraction,  and  when 
we  say  gold  we  mean  silver  as  well,  only  using  the 
term  gold  to  avoid  repetition  of  the  words  gold  and 
silver. 

Coarse  gold  requiring  longer  time  for  treatment  by 
cyanide,  it  is  better  if  possible  to  save  what  can  be 
saved  by  amalgamation,  and  this  latter  would  proba- 
bly be  followed  because  of  the  ease  with  which  the 
bullion  can  be  recovered  from  mercury. 

When  such  coarse  gold  occurs  in  conjunction  with 
fine  gold  or  auriferous  sulphurets,  it  is  customary 
to  crush  wet,  amalgamate  in  the  stamp-mill  mortar, 
pass  the  tailings  into  percolators  or  vats,  which 
are  provided  with  overflow-pipes  to  conduct  the 
excess  of  water  into  a  sump,  from  which  it  may  be 
returned  into  the  battery  to  be  used  again.  In  order 
to  save  a  portion  of  the  gold  lost  by  amalgamation  it 
has  been  customary  to  use  concentrators,  which  save 
the  metal  grains  containing  gold  and  allow  the  sand 
to  run  off  in  the  water.  Tailings  thus  greatly  re- 
duced in  bulk  can  be  shipped  to  smelters  or  treated 


1 8  CYANIDE  PROCESSES. 

again  with  mercury;  the  latter  method  will  not  prove 
very  effective,  however. 

It  is  possible  to  treat  these  concentrates  by  cya- 
nide, but,  being  generally  richer  in  metal,  their  treat- 
ment requires  longer  time  for  the  best  results.  As 
their  quantity  is  limited,  the  size  of  the  plant  need 
not  be  as  extensive  as  where  the  whole  mass  of  tail- 
ings is  to  be  treated.  Agitation  will  hasten  the 
operation  with  concentrates.  Percolation  with  con- 
centrates requires  20  days,  because  of  the  difficulty  the 
solution  encounters  in  passing  through  the  coarse  par- 
ticles of  ore.  "  Difficulty  sometimes  arises,  owing  to 
the  crystalline  form  of  iron  pyrites  and  galena.  These 
minerals  crystallize  in  cubes,  and  in  fluid  arrange 
themselves  face  to  face,  so  that  a  section  of  such  a 
mass  depostied  from  fluid  would  resemble  a  brick  wall 
in  structure."  Dr.  A.  Scheidel  suggests  mixing 
coarse  sand  with  the  cubes  to  overcome  the  difficulty. 
(See  "General  Information.") 

The  results  of  the  experiments  made  upon  tailings 
containing  sulphurets  by  the  State  Bureau  of  Mining 
of  California  are  here  given.  A  i-per-cent  solution 
of  potassium  cyanide  was  used  for  the  experiments. 

The  experiments  illustrate  the  effect  of  time  and 
strength  of  the  solution,  while  they  also  illustrate  that 
the  solution  is  not  impaired  in  its  action  when  sul- 
phides only  are  present,  both  of  which  are  important 
items  in  considering  the  scope  of  the  process. 


CYANIDE   PROCESSES.  19 

Treatment  lasting  2  hrs.  :  tailings  retained  35.29$  gold. 

3  "  *'  ,        "  31-37*  » 

4  M  ¥  «  30.37$  « 
6  M  "  «  25.49$  M 
8  "  "  "  21.56$  " 

Another  portion  from  the  same  lot  of  sulphurets 
ground  and  passed  through  a  loo-mesh  screen  (the 
former  having  been  passed  through  6o-mesh  sieve) 
were  then  treated  six  hours.  There  was  left  in  the 
tailings  after  this  treatment  17.64  per  cent  of  gold, 
showing  that  fineness  of  the  ore  in  this  case  materially 
aided  digestion. 

To  ascertain  whether  dilute  cyanide  would  extract 
all  the  gold  in  these  sulphurets  the  ore  was  ground  in 
an  agate  mortar  to  impalpable  powder,  and  digested 
or  48  hours  with  three  different  solutions  of  I  per 
cent  cyanide,  after  which  treatment  the  tailings  were 
found  to  contain  9.8  per  cent  of  gold. 

Another  lot  of  sulphurets  from  which  free  gold 
had  been  removed  with  great  care  was  subjected  to  a 
i-per-cent  solution  after  passing  i2O-mesh  screen. 

Treatment  lasting  2  hrs.  :  tailings  retained  31.2$  gold. 

3  M  "  »  28.5$     H 

4  "  "  "          15.6$    " 
-*.    5     "           "           "         15.5$    " 

8     "  "  "         10.4$    " 

The  deductions  to  be  made  by  comparison  with  the 


2O  CYANIDE   PROCESSES. 

6o-mesh  screen  experiments  are  that  double  the  fine- 
ness lessens  the  time  by  one  half  in  treatment  of  ore 
by  cyanide  solutions  of  the  same  strength. 

We  have  so  far  arrived  at  the  following  conclusions 
regarding  the  necessity  for  oxygen  and  the  strength 
of  solutions: 

1.  That   oxygen  is  necessary  for  dissolving  gold  in 
cyanide  of  potassium  solution,  and  that   it  combines 
with  the  potassium  of  the  potassium  cyanide  in  the 
proportions  stated  in  Eisner's  equation. 

2.  That  agitation  shortens  the  process,  as  does  the 
strength  of  the  solution,  but   that  what   is  gained   in 
time  is  lost  in  power  and  cyanogen. 

3.  That  weak  solutions  of  cyanide  of  potassium  are 
preferable  to   strong  solutions,  inasmuch  as  they  are 
less    prone    to    attack    base    metals,    and    are    more 
economical  in   proportion   to   loss   of  cyanide  during 
the  operation. 

4.  That    while    theoretically    one    part  of    cyanide 
should    dissolve    one    and    one    half    parts    of    gold, 
practically  the  operation   may  require  forty  parts  of 
cyanide  to  one  part  of  gold. 


CHAPTER  IV. 

CHEMISTRY  OF  THE   OPERATION. 

BEFORE  the  introduction  of  the  cyanide  process 
Plattner's  method,  with  its  improvements  by  Messrs. 
Thies,  Rothwell,  and  others,  was  the  only  economical 
chemical  process  used  on  a  commercial  scale.  The 
Russell  process  has  found  some  advocates,  but  the 
methods  of  cyanide  and  chlorination  have  found 
more.  The  cloud  which  hovered  over  all  chemical 
operations  for  the  extraction  of  the  precious  metals, 
and  which  exists  to-day,  was  due  to  frauds  and  un- 
practical schemes.  Chemists  have  also  made  tests  in 
their  laboratories,  and  have  induced  parties  to  adopt 
their  plans,  which  have  proved  to  be  valueless  upon  a 
commercial  scale. 

To  obtain  economical  and  practical  methods  sim- 
plicity must  be  one  of  the  chief  objects. 

It  is  of  no  value  that  one  can  extract  all  the  gold 
from  an  ore  if  the  cost  of  extraction  is  more  than  the 
gold  recovered. 

While  the  cheapest  piece  of  machinery  is  not 
always  the  best,  the  simplest  and  cheapest  piece  of 
mechanism  which  will  do  the  work  satisfactorily  is  the 

21 


CYANIDE  PROCESSES. 

best.  The  scope  of  a  chemical  process  is  another 
consideration ;  that  process  which  will  meet  every  re- 
quirement has  not  been  found,  but  the  cyanide  proc- 
ess has  approached  nearer  to  the  ideal  than  any  we 
have  knowledge  of. 

The  chemical  reaction  of  the  cyanide  process  is 
such  that  after  the  chemist  has  determined  the  pro- 
portions of  chemicals  to  be  used  in  the  treatment  of 
any  particular  ore  the  entire  work  becomes  mechanical. 

The  process  may  be  adapted  to  wet  or  dry  crush- 
ing; to  coarse  or  fine  ore,  according  to  the  texture  of 
the  ore ;  to  tailings  or  concentrates  from  other  treat- 
ment. It  is  not  applicable  to  every  ore,  but  to  what 
ores  it  may  be  applied  we  can  readily  determine  by 
analysis.  Mr.  Paul  says  that  "if  laboratory  tests 
were  satisfactory  on  50  per  cent  of  ore  he  would  not 
hesitate  to  build  a  mill  on  that  test,  so  uniform  are 
the  results  to  be  obtained." 

The  chemical  reaction  expressed  by  Eisner's  equa- 
tion is  for  gold : 

2'Au  +  4KCy  +  O  +  H2O  =  2AuKCy2  +  2KOH. 
For  silver: 

2Ag  +  4KCy  +  O  +  H2O  =  2AgKCy2  +  2KOH. 

From  the  equations  it  is  seen  that  double. salts  of 
gold  and  silver  are  formed  with  potassium  cyanide, 
while  caustic  potash  is  liberated.  It  is  yet  an  open 


CYANIDE   PROCESSES.  23 

question  whether  gold  is  found  otherwise  than  in  a  free 
state  in  ores,  and  it  is  given  as  a  reason  why  gold 
unites  so  readily  with  cyanides  that  it  is  in  a  free 
state. 

Silver  is  found  more  in  combination  with  chemical 
compounds  in  gold  ores,  and  hence  is  not  recovered 
as  readily  as  gold.  Furthermore,  the  sulphides  of 
zinc  and  other  base  metals  generally  accompanying 
gold  and  silver  in  refractory  ores  are  not  acted  upon 
by  cyanide  solutions,  at  least  so  as  to  be  noticeable. 

There  are  acid  ores  containing  oxidized  pyrites  or 
acid  earths  which  are  very  destructive  to  cyanide  and 
must  be  treated  before  being  introduced  to  the 
cyanide  solution.  Ores  or  tailings  containing  sul- 
phurets  subjected  to  the  weather  will  oxidize,  forming 
metallic  sulphates  on  the  earthy  constituents.  These 
are  only  partially  soluble  in  water,  so  that  while  water 
washings  will  assist  in  removing  them,  other  treat- 
ment should  follow.  The  cyanide  would  partially  be 
absorbed  and  partially  decomposed  by  these  sub- 
stances if  the  ore  were  not  freed  from  their  influences, 
as  illustrated  in  the  following  equations : 

I.          FeSO4  +  2KCy  =  FeCy2  -f  K2SO4 . 

Were  lime  added  before  the  potassium  cyanide,  we 
we  could  expect  the  following  reaction : 

2FeSO4  +  2CaO  =  gFeO  -f-  20180, .  f» 


24  CYANIDE   PROCESSES. 

Ferrous  oxide,  while  a  powerful  base,  and  neutral- 
izing acid,  absorbs  oxygen  readily,  passing  into  ferric 
oxide,  thus: 

2FeO  +  O=  Fe2O3. 

This  being  a  very  feeble  base,  it  will  have  no 
further  effect,  and  will  undoubtedly  be  partially 
removed  from  the  ore  by  the  water  wash  necessary  to 
carry  off  the  calcium  sulphate.  [^/MacArthur  states 
that  I  part  of  lime  is  sufficient  for  99  parts  of  ore  for 
this  treatment.  We  would  advise,  however,  labora- 
tory and  litmus-paper  tests  for  surety. 


II.      F 

=  Fe,0.  +  3(K.SO.)  +  6HCy. 

From  this  equation  we  see  that  ferric  sulphate  is 
converted  into  ferric  oxide,  and  potassium  sulphate 
with  free  hydrocyanic  acid  liberated  as  well. 

The  action  of  sulphates  of  alumina  and  magnesia  is 
practically  the  same  with  cyanide,  liberating  free 
hydrocyanic  acid,  which  is  a  loss.  To  neutralize 
these  sulphates  we  give  the  ore  a  preliminary  treat- 
ment as  before,  using  lime  or  sodium  oxide,  — 

Fea3(S04)  +  3Na20  =  Fe2O3  +  3(Na2SO4),- 

and  then  follow  it  with  a  water  wash  to  remove  the 
precipitants  from  the  ore,     While  ferrous  salts,  solu- 


CYANIDE   PROCESSES.  2$ 

ble  or  insoluble,  exist  in  the  ore,  the  lime  or  soda 
will  combine  with  the  acid  to  deposit  the  ferric  oxide. 
The  ferric  oxide,  although  a  feeble  base,  woul^l  com- 
bine with  cyanogen  to  a  more  or  less  extent, *so  that 
if  it  can  be  freed  from  the  ore  so  much  the  better. 
Where  sulphates  of  alkaline  earths  exist  only,  the 
oxidation  may  take  place  with  the  cyanide  solution 
in  contact,  but  this  is  not  advisable  where  lime  is 
present.  The  quantity  of  alkali  presented  for  neu- 
tralizing acid  ores  must  be  determined  by  laboratory 
tests  of  the  ore,  as  demonstrated  under  "Laboratory- 
work."  The  tests  having  determined  the  amount  of 
alkali  needed,  the  proper  quantity  is  not  added  all  at 
once,  but  little  by  little,  so  that  its  action  will  be 
uniform  throughout  the  ore  being  treated. 

Butters  and  Clennell  advanced  the  following  equa- 
tions as  possible  reactions  accompanying  the  action  of 
cyanide  on  pyrites : 

III.  To  illustrate  the  influence  of  oxygen  on  ferric 
sulphides  or  iron  pyrites : 

(a)  FeS2  +  H20  +  ;O  =  FeSO4  +  H2SO4 . 

Iron  sulphate  and  free  sulphuric  acid  are  formed  by 
this  action.  Should  the  iron  sulphate  be  further 
attacked  by  oxygen  from  the  air,  we  could  expect 

(b)  2FeS04+0=Fe203,2S03, 
which  is  an  insoluble  basic  sulphate  (Wittstein). 


26  CYANIDE   PROCESSES. 

Berzelius  gives  the  action  on  ferrous  sulphate  by 
the  oxygen  of  the  air  as 

ioFeSO4+  5O  =  2Fe2O8,2SO3  +  3Fe2(SO4)3. 

The  sulphate  being  converted  into  insoluble  basic 
sulphate  and  soluble  ferric  sulphate.  The  cyanide 
reaction  on  the  ferrous  salts  is  given  as  follows  : 

IV.       FeSO4  +  2KCy  =  FeCy,  +  K2SO4  . 
The  reaction  then  continued  results  in 
FeCy,  +  4KCy  =  K.FeCy., 
ultimately  giving  rise  to 


=  Fe.O,  +  6K2SO,  +  Fe,Cy,.  . 

Should  lime  be  present,    the    reaction   would  not    be 
complete.      Taking  the  double  salt,  as  follows,  — 

First,  FeCy2+  4-KCy  =  K4FeCyfl,- 
Second,  K4FeCy6+Ca(OH)2 

=  2KOH  +  FeCy2+  2KCy  +  CaCy,. 

V.    Ferric  salts  and  cyanide  give 

Fe5(SO,),+  6KCy  =  Fe,Cy.+  3K2SO.    and 
Fe,Cyt  +  6H,0  =  Fe,(OH)8  +  6HCy, 
Fe,(S64)r+6KCy+6HI0 

=  Fc,fOH),  +6HCy  +  3K,SO,  . 


CYANIDE   PROCESSES,  2? 

A  mixture  of  ferrous  and  ferric  salts  on  addition  of 
cyanide  of  potassium  gives  the  well-known  Prussian 
blue  when  ferric  salt  is  in  excess,  thus: 

VI.    iSKCy  -f  3FeS04  +  2Fe2(SO<)3 

=  9K,S04-fFe4Fe3Cy,8. 

By  mixture  of  the  same  salts  with  ferrous  salt  in 
excess  we  obtain  Turnbulls  blue  : 


VII.    i2KCy  +  3FeS04+Fe,(S04), 

=  6K1S04  +  FeiFeiCyH. 

The  reactions  between  iron  and  potassium  cyanide 
are  very  complicated  and  they  are  not  fully  under- 
stood, yet  we  can  understand  from  the  foregoing 
combinations  that  loss  of  cyanide  will  take  place,  so 
that  the  more  safeguards  used  to  prevent  loss  will 
prove  economical  and  beneficial. 

If  iron  be  present  in  the  solution  of  gold  and 
cyanide  of  potassium,  the  following  possibility  may 
occur: 


6AuKCy2  +  6KHO  +  2Fe  +  sH.O 

=  6AuKCy  +  6HCy  +  6KHO  +  Fe2O3. 


In  this  equation,  however,  the  free^  cyanic  acid 
would  combine  at  once  with  the  free  alkali  to  form 
potassium  cyanide  : 

6HCy  +  6KHO  +  Fe2O3  =  6KCy  +  6H2O  +  FefO,. 


28  CYANIDE   PROCESSES. 

This   reaction   shows   that   if  a  metal  be  present  it 
may  be  the  means  of  regenerating  potassium  cyanide. 
We    are    inclined   to   believe   that   this   action  is  one 
cause   for   so   little   loss  of  cyanide  when  the  electro 
cyanide  process  is  used. 

The  more  recent  practice  is  to  mix  with  the  cyanide 
solution  sodium  oxide  to  reduce  any  acid  present  or 
formed,  and  thus  reduce  the  amount  of  cyanide  con- 
sumed. J.  C.  Montgomerie  uses  NaOH,  Na2O,  and 
Na2O.2  with  equally  satisfactory  results.  His  propor- 
tions of  cyanide  potassium  to  the  ore  to  be  treated 
are  3  Ibs.  of  cyanide  to  the  ounce  of  gold  ;  3/4  by 
weight  of  sodium  to  the  cyanide  used.  These  are  dis- 
solved separately  in  a  little  water,  then  mixed  together 
in  water  of  sufficient  quantity  to  treat  the  ore. 

Novices  should  study  the  subject  of  sodium  before 
mixing  with  water. 


CHAPTER    V. 

LEACHING  THE  ORE. 

THE  original  ideas  of  MacArthur-Forrest  were  to 
agitate  the  ore  in  the  cyanide  solution ;  when  we  say 
ore,  tailings  are  included  in  the  term.  They  suggested 
no  form  of  vessel  or  mechanical  means,  but  simply 
said  that  if  the  pulp  were  kept  in  motion  by  any  con- 
venient mechanical  stirrer  the  operation  would  be 
hastened.  Agitation  should  be  continued  until  the 
gold  and  silver  are  nearly  all  dissolved,  when  the 
liquor  containing  the  precious  metals  is  to  be  drawn 
off  for  precipitation. 

Rae's,  Simpson's,  and  nearly  every  electrical  cyanide 
system  for  the  cyanide  process  is  conducted  on  the 
lines  of  agitation.  It  is  conceded  that  agitation 
lessens  the  time  of  extraction  and  expedites  the  proc- 
ess. It  allows  the  oxygen  of  the  atmosphere  to  act 
on  the  potassium,  freeing  the  cyanogen  so  that  it  may 
unite  with  the  gold ;  it  is  also  probable  that  by  agita- 
tion the  cyanide  can  come  into  contact  with  the  metals 
with  greater  ease :  thus  with  tarnished  particles  of 
gold  or  gold  covered  with  a  sulphide  film  the  slighest 

scratch  would  admit  of  the  cyanide  attacking  it,  and  so 

29 


30  CYANIDE   PROCESSES. 

dissolving  it  in  quicker  time.  Where  ores  are  coarse 
and  porous,  agitation  would  assist  the  operation,  but 
its  great  practical  use  will  be  found  with  ores  hard  and 
fine.  Where  very  low-grade  tailings  are  treated,  or 
where  fuel  is  expensive  and  unhandy  to  be  obtained, 
or  where  very  large  vats  and  ore  charges  are  used, 
mechanical  agitation  may  prove  more  expensive  than 
simple  percolation. 

Ores  containing  tellurides,  arsenides,  and  sulphides 
will  give  better  results  if  agitated  than  can  be  obtained 
by  percolation.  Barrels  with  arms,  similar  in  con- 
struction to  chlorinating-barrels,  have  been  used ;  also 
shafts  with  radiating  arms,  and  barrels  simply  rotated, 
for  the  purpose  of  agitation.  The  size  of  ore- charges 
treated  is  limited  to  the  capacity  of  the  barrels  in 
one  case  and  the  size  of  the  vats  and  motive  power  in 
the  other. 

If  time  be  an  element  of  importance,  stronger  solu- 
tions of  cyanide  may  be  employed  with  agitation,  but 
as  the  loss  is  proportionally  greater,  it  is  the  customary 
practice  to  use  weaker  solutions  and  economize  on 
chemicals.  With  agitation-barrels  it  is  necessary  to 
introduce  chemical  oxidizing  agents,  otherwise  no  time 
will  be  gained,  as  has  been  illustrated  by  MacLaurin's 
experiments. 

The  percolating  process  is  extensively  employed  in 
South  Africa,  where  ores,  concentrates,  and  tailings,  are 
worked  by  it.  This  process  is  used  as  well  in  other 


CYANIDE   PROCESSES.  31 

countries,  and  consists  in  soaking  the  ores  to  be 
treated  in  cyanide  of  potassium  solutions.  After 
soaking  or  leaching,  as  it  is  called,  the  solution  is 
drawn  off  and  another  stronger  solution  run  on. 

As  we  have  shown,  the  time  required  for  running 
or  draining  these  various  leaching  solutions  from  the 
ores  depends  upon  the  degree  of  fineness  of  the  ore 
and  its  character  for  packing  tight,  which  of  course 
would  hinder  the  rapidity  of  drainage. 

Here  it  can  be  seen  that  uniformity  of  crushing  is 
advantageous,  and  that  the  coarser  the  ore  the  quicker 
will  be  the  drainage.  The  liquor  is  run  into  the 
vat  through  the  bottom  by  a  pipe  connected  with  a 
vat  holding  the  solutions  of  various  strengths.  The 
solution  rises  slowly  upwards,  percolating  the  ore  in 
its  upward  movement,  until  it  has  covered  the  entire 
charge  of  ore  in  the  vat.  The  object  of  this  upward 
percolation  against  gravity  is  that  by  this  means 
it  permeates  the  mass  evenly ;  It  is  run  in  slowly  to 
avoid  making  channels  in  the  ore,  which  would  be  dis- 
advantageous to  good  downward  percolation  when 
drainage  takes  place.  The  idea  is  to  make  the  whole 
quantity  of  liquor  rise  and  fall  through  the  ore  evenly, 
and  not  up  or  down  through  channels. 

When  tailings,  especially  clayey  tailings,  are  charged 
intovats,  they  are  apt  to  remain  lumpy.  Cyanide  solu- 
tion will  have  difficulty  in  penetrating  such  masses,  as 
channels  will  be  formed  and  the  liquor  will  naturally 


3 2  CYANIDE   PROCESSES. 

go  the  easiest  way  through  the  ore.  A  mixture  of 
clean  sand  with  the  ore  will  assist  the  percolation  in 
such  cases,  and  this  proceeding  may  be  absolutely 
necessary  with  clayey  tailings  which  would  pack  with- 
out agitation  and  effectually  prevent  percolation.  The 
process  for  cyanide  treatment  is  conducted  to  this 
point  as  follows: 

The  ore  in  every  instance  is  or  has  been  crushed. 
It  is  then  charged  into  a  vat.  If  sulphates  or  other 
acid  salts  are  present  which  would  be  injurious  to 
potassium  cyanide,  the  ore  is  allowed  to  stand  in 
water,  or  water  containing  enough  caustic  alkali  to 
neutralize  the  acid.  This  water  is  now  drained  off 
and  wash-water  added.  b . 

After  the  wash-water  has  drained  off,  the  first  solu- 
tion of  cyanide,  containing  from  0.02  to  0.08  per  cent 
potassium  cyanide,  is  allowed  to  percolate  through 
the  ore  and  stand  some  hours  before  draining. 

The  standard  or  strong  solution  is  next  percolated 
through  the  ore  and  drained  off.  After  this  another 
weak  solution  is  percolated  through  the  ore  and 
drained  off,  and  this  last  solution  is  followed  by  a 
water  wash  to  take  up  any  cyanide  containing  gold 
that  remains  in  the  ore. 

The  first  weak  solution  is  allowed  to  remain  in 
contact  with  ore  12  hours. 

The  standard  solution  is  allowed  to  remain  in  contact 
12  hours,  and  has  a  strength  from  O.J  to  1.5  per  cent. 


CYANIDE  PROCESSES.  33 

The  final  weak  solution  is  run  on  after  the  ore  has 
been  exposed  to  the  air  4  hours,  and  is  allowed  to 
remain  about  12  hours.  The  final  weak  solution  has 
a  strength  of  from  0.02  to  0.04  per  cent.  The 
quantity  of  solutions  used  is  one  half  a  ton  for  each 
ton  of  ore. 

The  solutions  of  cyanide  and  gold  are  run  from  the 
vats  into  filter-boxes  and  from  there  into  sumps,  to  be 
used  again  as  weak  solutions  or  else  brought  up  to 
the  standard  of  strong  solution  by  addition  of  KCy. 

Having  obtained  the  gold  from  the  ore  in  potas- 
sium cyanide  solution  the  next  step  is  the  recovery  of 
the  gold  from  the  solution  by  precipitation.  Mac- 
Arthur's  first  patent  suggests  the  evaporation  of  the 
solution  to  dryness,  and  fusing  the  resulting  saline 
residue,  or  by  treating  the  residue  with  sodium  amal- 
gam. Any  one  acquainted  with  evaporation  on  a 
small  plan  knows  how  tedious  such  methods  are. 

The  treating  of  the  residue  with  sodium  amalgam 
would  also  be  unsatisfactory,  as  the  mercury  would 
oxidize  quickly  and  refuse  to  unite  with  the  gold. 

MacArthur  was  quick  to  see  the  crudeness  of  these 
methods,  but  by  careful  experiments  with  zinc  finally 
ascertained  fine  filiform  threads  of  zinc  would  precipi- 
tate the  gold  in  metallic  state.  Thin  zinc  shavings 
are  cut  from  disks  of  zinc  turned  in  a  lathe.  The 
precipitation-boxes  are  filled  with  these  zinc  shavings, 
and  are  so  connected  together  in  a  series  that  the 


34  CYANIDE   PROCESSES. 

solution  will  go  into  the  first  box  at  the  bottom,  rise 
up  through  the  zinc  sponge  until  it  reaches  an  orifice, 
when  it  flows  into  the  next  box  of  the  series  from  the 
bottom  up,  and  so  on.  The  first  solution  in  passing 
through  the  zinc  filter  does  not  precipitate  the  gold 
as  fast  as  the  strong  solution,  but  its  action  on  the 
zinc  paves  the  way  for  quick  precipitation  of  the  gold 
in  the  strong  solution.  The  action  on  zinc  is  slow, 
but  increases  in  intensity  after  it  has  commenced. 
Zinc  plates  or  granulated  zinc  will  not  answer  for 
precipitation  :  the  zinc  must  be  in  thin  shavings. 
Pure  zinc  will  not  decompose  pure  potassium  cyanide 
rapidly  until  some  caustic  is  formed  ;  but  as  soon  as 
iron  or  gold  is  in  contact  with  zinc  and  a  cyanide 
solution,  evolution  of  hydrogen  commences  at  once. 

Hydrogen  formed  in  the  precipitation-box  shows 
that  electric  action  is  going  on  between  the  metal  and 
the  solution,  in  which  there  is  an  exchange  ;  thus, 

2  AuKCy2  +  Zn  =  K2ZnCy4  +  2  Au. 


Alkali  metals  will  precipitate  gold  from  the  cyanide 
solution.  Mr.  Malloy  patented  a  process  which,  if 
successful,  is  superior  in  point  of  recovery  to  zinc 
precipitation,  since  the  potassium  cyanide  is  regener- 
ated while  gold  is  set  free  in  mercury,  from  which  it 
can  be  recovered  readily  compared  with  the  recovery 
from  zinc. 


CYANIDE   PROCESSES.  35 

JMalloy  uses  sodium  or  potassium  amalgam,  formed 
electrolytically  from  a  solution  of  carbonate  in  contact 
with  a  bath  of  mercury.  The  alkali  metal  combines 
with  cyanogen  of  the  gold  compound,  forming  an 
alkali  salt  of  cyanogen,  while  the  gold  is  instantly 
amalgamated.  Thus, 

K2CO3  +  elect,  current  =  K2  +  CO,  +  OH2 
KAu  +  Cy,  +  K  =  Au  +  2KCy. 

If  this  method  prove  successful,  it  should  add 
greatly  to  the  cyanide  process  as  an  economical  gold 
extractor,  for  it  will  save  cyanide,  and  also  recover 
finer  bullion  in  a  very  much  easier  form  to  handle. 

Dr.  Johnston  precipitates  the  gold  and  silver  from 
the  cyanide  solution  by  pulverized  charcoal,  through 
which  it  is  filtered.  By  one  filter  he  recovers  25  per 
cent  of  the  gold ;  by  a  series  of  filters  he  recovers  95 
per  cent.  The  gold  and  silver  is  recovered  by  smelt- 
ing with  fluxes  after  the  charcoal  has  been  disposed 
of  by  burning. 

Attempts  have  been  made  to  precipitate  the  gold 
by  use  of  zinc  and  sodium  amalgams,  the  object  being 
to  save  cyanide  and  obtain  the  precious  metals  in  the 
form  of  amalgam  for  recovery.  Fairly  good  results 
have  been  obtained  this  way. 

F.  Rinder's  process  is  to  precipitate  the  precious 
metals  by  chloride  of  zinc.  The  gold  is  obtained  as  a 
grayish  powder,  by  slowly  dropping  the  chloride  of 


36  CYANIDE  PROCESSES. 

zinc  into  the  solution.  The  precipitate  is  collected, 
dried,  and  finally  melted  into  bullion.  To  obtain  the 
gold  and  sjlver  separately,  the  solution  is  treated  first 
with  sulpht?e  of  iron  or  sodium  to  separate  the  silver 
and  precipitate  it.  The  solution  containing  the  gold 
is  now  filtered  off  fromthis  precipitate,  and  the  gold 
precipitated  by  *rtripba£«  of  zinc.  The  cyanide  liquor 
can  now  be  reinforced  and  used  again. 

Precipitation  by  electrical  action  is  considered  in 
the  second  part,  under  the  proper  heading. 

Moldenhauer  uses  aluminum  as  a  precipitant,  which 
he  claims  does  the  work  without  entering  into  com- 
bination with  cyanogen.  He  expresses  his  process  as 
follows : 


I.  6Au+i2KCy+  3O 

=  6AuKCy2  +  6KHO  +  sH2O. 

If  to  this  cyanuret-of-gold  solution,  which  contains 
free  alkali,  aluminum  is  added,  the  following  reaction 
takes  place  : 


II. 

=  6Au  +  6KCy  +  6KHO  +  A1,O3- 

4  : 

The  hydrocyanic  acid  combines  at  once  with  the 
caustic  potash  to  form  potassium  cyanide.     Thus  the 
,   second  member  of  equation  II  would  be 

i 


CYANIDE  PROCESSES.  37 

6Au  +  i2KCy  +  6H2O  +  A13O3> 

and  cyanide  is  regenerated. 

In  another  instance  he  precipitates  the  gold  and 
regenerates  the  cyanide  by  an  alkaline  earth,  which 
may  be  added  after  precipitation  by  aluminum,  pro- 
vided a  solution  is  used  which  contains  a  free  acid  and 
not  a  free  alkali. 


CHAPTER  VI. 

ZINC  AS  A  PRECIPITANT. 

THE  objections  to  the  use  of  zinc  as  a  precipitant 
are  such  as  to  create  considerable  comment.  It  is 
considered  too  expensive  by  some,  because  of  the 
loss  of  cyanide  in  the  zinc-precipitating  boxes,  and 
because  it  requires  so  much  zinc.  Others  consider  it 
from  a  different  standpoint,  namely,  that  the  recovery 
of  bullion  from  its  use  is  too  coarse,  and  the  recovery 
by  refining  too  complicated,  together  with  a  certain 
loss  of  gold  and  silver  due  to  refining  those  metals 
with  zinc.  The  numerous  methods  suggested  do  not 
seem,  however,  to  have  driven  the  zinc-precipitating 
process  to  the  wall,  although  we  expect  to  see  it  ac- 
complished in  time. 

"  Examination  of  precipitants  from  a  cyanide  mill, 
consisting  of  gold,  silver,  copper,  calcium  carbonate, 
and  fine  shreds  of  zinc,  showed  that  copper  was  not 
in  a  metallic  state,  because  it  dissolved  with  effer- 
vesence  in  dilute  HC1."  Mr.  Eichbaum  observed 
that  zinc  does  not  precipitate  copper  from  a  solution 
made  with  potassium  cyanide  98  per  cent  purity ;  but 

38 


CYANIDE   PROCESSES.  39 

on  adding  iron  a  brisk  evolution  of  gas  took  place, 
but  no  copper  was  precipitated.  If  an  impure  cyanide 
solution  is  used,  copper  is  soon  deposited  upon  the 
zinc,  which  is  no  doubt  due  to  caustic  or  carbonate 
in  the  solution. 

The  solution,  after  gold  has  been  deposited,  contains 
zinc,  yet  the  solution,  after  being  used  for  months, 
does  not  cause  inconvenience.  By  the  addition  of  water 
the  zinc  could  not  saturate  the  solution,  and  the  same 
is  true  of  alkali  carbonate,  which,  in  the  absence  of 
lime,  is  continually  forming.  The  white  precipita«*»'tf* 
is  the  result  of  alkali  on  zinc,  and  the  zinc  potassic 
oxide  on  the  double  cyanide  of  zinc  and  potassium, 
as  shown  by  the  formula,  and  which  is  insoluble. 
This  double  cyanide  of  zinc  and  potassium  being  used 
over  again  in  the  percolating  vats,  forms,  with  the  iron 
salts  in  the  ore,  ferrocyanide  of  zinc. 

Buckland  considers  this  the  reason  for  constant  re- 
moval of  zinc  from  the  solution  with  the  residues. 

This  double  cyanide  of  zinc  and  potassium  formed 
during  precipitation  of  gold  is  not  available  for  dis- 
solving gold  in  new  operations,  but  it  does  not  appear 
to  be  detrimental  to  the  process  when  new  cyanide 
solution  is  added  to  it.  It  does  not  precipitate  gold 
dissolved  by  a  new  solution  of  cyanide. 

Auro-potassium-cyanide  seems  to  be  a  very  stable 
compound,  and  not  readily  decomposed,  as  is  evi- 
dent when  we  see  that,  being  once  deposited  on  zinc, 


4°  CYANIDE  PROCESSES. 

the  gold  does  not  become   redissolved  by  excess  of 
cyanide  so  long  as  zinc  is  present. 

We  should  think  that  if  gold  is  readily  deposited 
from  potassium  cyanide  solution  by  aluminum,  zinc 
could  be  as  well,  in  which  case  the  cyanide  would  be 
regenerated.  Thus, 

6ZnKCya  +  6KHO  +  sH2O  +  2A1 

=  6Zn  +  6KCy  +  6HCy  +  6HKO  +  AlaO3 
=  6Zn  +  i2KCy  +  6HaO  +  A1SO3- 

Zinc  for  precipitation  must  not  contain  arsenic,  an- 
timony, or  lead,  although  a  small  percentage  of  the 
latter  is  not  injurious.  MacArthur's  results  from  zinc 
tests  were  that  fine  zinc  shavings  answered  the  pur- 
pose better  than  zinc  in  any  other  form.  Granulated 
zinc  and  zinc  sheets  produced  unsatisfactory  results, 
due  possibly  to  the  limited  surface  offered  for  attack, 
or  possibly  due  to  the  slow  action  of  cyanide  on  zinc 
in  compact  form,  the  same  as  its  slow  action  on  gold 
in  grains. 

We  are  inclined  to  this  latter  belief,  and  consider 
that  it  attacks  the  shavings  because  they  offer  numer- 
ous uneven  surfaces  or  particles  which  the  cyanide 
can  attack  readily.  As  before  stated,  while  the  action 
is  slow  at  first,  it  becomes  quite  vigorous  and  rapid 
as  it  proceeds. 

Zinc  dust  is  objectionable,  as  it  would  pack  and  also 


CYANIDE   PROCESSES.  41 

become  mixed  with  other  impurities,  which  would 
afford  obstacles  to  refining  the  bullion. 

Zinc  amalgam  does  not  afford  surface  enough  for  its 
weight,  and  the  method  of  adding  it  to  the  solution 
in  small  pills,  so  to  speak,  is  too  tedious  and  faulty. 
The  precipitation  of  the  metals  in  the  zinc-boxes 
takes  place  rapidly,  and  as  the  first  series  of  boxes 
do  most  of  the  work,  the  zinc  is  consumed  faster  in 
them.  This  zinc  is  replaced  by  the  zinc  from  the  last 
boxes  of  the  series,  and  the  last  boxes  filled  with 
fresh  zinc.  The  object  aimed  at  is  to  have  the  dep- 
osition of  gold  commence  at  once,  which  would  not 
be  the  case  with  fresh  zinc ;  besides,  the  few  particles 
of  gold  adhering  to  the  zinc  in  the  last  boxes  are 
brought  to  the  place  where  the  greater  part  of  the 
gold  is  precipitated. 

According  to  theory,  one  pound  of  zinc  should  pre- 
cipitate six  pounds  of  gold.  However,  various  losses 
occurring,  such  as  generation  of  hydrogen,  formation 
of  potassium  zinc  cyanide,  formation  of  zinc  carbo- 
nate, and  the  loss  which  occurs  from  sifting  the  gold 
and  ridding  it  of  zinc,  makes  the  total  loss  of  zinc  to 
gold  precipitated  sixteen  to  one  practically.  That  the 
amount  of  zinc  used  will  vary  at  different  operations 
we  can  as  readily  expect  as  that  different  amounts 
of  coal  will  be  consumed  under  different  boilers. 
One  cubic  foot  of  zinc  shavings  is  said  to  be  sufficient 
for  the  precipitation  of  gold  from  two  tons  of  solu- 


42  CYANIDE   PROCESSES. 

tion  in  twenty-four  hours  at  some  works.  One  cubic 
foot  of  zinc  shavings  weighs  from  three  to  six  pounds, 
and  exposes  forty  square  feet  of  surface  per  pound. 
MacArthur  says:  "Improvements  in  detail  to  in- 
crease the  surface  and  decrease  the  weight  of  the 
zinc  have  enabled  him  to  obtain  threads  so  light  that 
one  pound  will  occupy  the  space  of  two  gallons." 
The  zinc  in  this  form  is  said  to  possess  enormous 
chemical  activity. 

After  passing  through  the.,  zinc-boxes  the  solution 
should  not  contain  50  per  tent  per  ton  of  gold  or 
hardly  a  trace,  since  this  gold  will  no  doubt  be  lost 
by  precipitation  from  the  weak  solutions. 


CHAPTER    VII. 

TREATMENT   OF   BULLION. 

HAVING  precipitated  the  gold  and  silver  from  the 
cyanide  solution,  the  next  process  is  refining  the  bull- 
ion. The  simplest  method  of  recovering  gold  from 
the  ore  is  by  amalgamation  with  mercury.  The  mer- 
cury is  then  pressed  through  a  cloth  or  chamois-skin, 
the  gold  amalgam  remaining  in  the  cloth  or  skin. 
This  is  then  placed  in  a  retort  and  the  mercury  dis- 
tilled from  the  gold ;  the  mercury  is  condensed  and 
saved  for  future  use.  When  the  cyanide  process  is 
used,  the  operation  is  much  more  complicated.  The 
zinc  with  the  gold  adhering  is  shaken  in  water,  when 
the  gold  and  zinc  fall  off  into  the  water.  The  water 
is  then  filtered,  and  the  fibrous  particles  of  zinc  may 
be  collected  in  a  sieve  and  shaken  again  to  remove 
the  gold.  This  last  sifting  removes  the  coarse  zinc 
from  the  mass  to  be  refined.  The  precipitate  will 
contain  gold,  silver,  and  zinc,  and  if  it  comes  from 
cleaning  up  of  zinc  filter-boxes  other  metals. 

This  precipitate  is  thoroughly  dried  and  roasted 
slowly,  care  being  taken  that  the  flame  does  not  come 
in  contact  with  the  mass.  After  being  thoroughly 

43 


44  CYANIDE    PROCESSES. 

dried  it  may  be  refined  by  the  "  calcining  and  roast- 
ing process"  or  recovered  by  the  "  acid  process." 

The  roasting  process  is  used  where  oxidation  of 
base  metals  has  not  been  complete.  At  Johnannis- 
burgh,  South  Africa,  the  acid  treatment  is  not  em- 
ployed, as  it  involves  washing  and  filtration  of  the 
slimes,  with  loss  of  gold  by  formation  of  regulus  in 
melting,  if  sulphates  remain  in  the  slimes,  by  fault  of 
imperfect  washing.  "The  practice  is  to  dry  the 
slimes  to  dust  nearly;  then  to  thoroughly  mix  them 
with  powdered  nitre,  the  amount  varying  from  3  to 
33  per  cent  of  their  weight,  and  the  mass  gently 
heated  on  a  wrought-iron  tray.  The  flames  must  not 
come  in  contact  with  the  slimes,  and  the  gases  should 
be  conducted  up  a  flue  away  from  the  operator.  By 
the  use  of  nitre  everything  connected  with  the  pre- 
cipitate is  refined.  After  this  oxidization  the  roasted 
mass  is  placed  in  plumbago  crucibles  with  the  proper 
fluxes." 

When  metallic  oxides  are  present,  the  flux  is:  six 
parts  roasted  nitre  slimes;  four  parts  borax;  two 
parts  soda ;  one  part  sand.  When  only  a  small  amount 
of  metallic  oxide  is  present,  the  charge  may  be  three 
parts  slimes,  one  part  borax,  two  parts  soda,  one  part 
sand.  The  function  of  the  sand  is  to  form  a  fusible 
slag  with  soda,  and  protect  the  pots  from  metallic 
oxides  and  potash  formed  by  the  reduction  of  the 
nitre.  The  slag  resulting  from  the  melting  of  these 


CYANIDE   PROCESSES.  45 

slimes  usually  contains  considerable  gold ;  it  is  there- 
fore crushed  and  sent  to  the  smelters.  It  is  some- 
times customary  to  pan  these  slags,  after  crushing, 
for  gold,  sending  the  tailings  to  the  smelter.  Fluxes 
which  give  clean  fluid  slag  are  preferable  in  this  as  in 
any  other  refining. 

For  the  sulphuric  acid  treatment  wooden  tubs  arc 
sufficient,  the  temperature  created  by  the  action  of 
the  acid  on  the  zinc  in  dissolving  it  being  sufficient  to 
discard  the  application  of  artificial  heat.  After  the 
zinc  has  dissolved  the  acid  solution  is  decanted,  and 
the  bullion  washed  to  remove  all  acid  traces. 

Should  any  zinc  remain,  its  presence  in  melting  will 
cause  loss  of  gold  by  evaporation,  as  the  zinc  volatilizes 
by  heat ;  it  may  be  better,  therefore,  to  treat  the  pre- 
cipitate first  with  a  weak  solution  of  acid,  then  follow 
it  by  a  stronger. 

After  washing  the  mass  is  dried  at  a  low  heat ;  when 
the  moisture  is  driven  off,  the  heat  is  increased  to  a 
dark  red.  After  one  hour's  roasting  all  oxidation 
of  the  base  metals  which  escaped  removal  by  acid 
treatment  should  be  complete,  the  mass  presenting  a 
brown-gray  appearance.  The  roasting  completed,  the 
bullion  is  transferred  to  a  wrought-iron  box  for  cool- 
ing purposes.  When  cool,  it  is  pulverized.  Borax 
and  soda  are  added  to  make  a  clear  slag.  Plumbago 
crucibles  are  well  adapted  for  this  treatment,  and 
borax  is  put  into  them  first ;  the  mixture  of  borax  and 


46  CYANIDE   PROCESSES. 

roasted  ore  is  put  in  from  time  to  time  as  the  mixture 
melts  and  sinks  down.  The  melting  goes  on  speedily 
and  in  the  most  satisfactory  manner.  After  the  whole 
quantity  is  charged  the  temperature  is  kept  high  for 
some  time  to  give  the  small  bullion  globules  time  to 
collect.  The  contents  of  the  crucible  are  then  poured 
into  a  heated  mould  and  allowed  to  cool.  It  is  claimed 
that  this  acid  treatment  has  advantages  over  the  cal- 
cining treatment,  being  simpler  and  allowing  the 
plumbago  crucibles  to  be  repeatedly  used ;  also  that 
the  bullion  is  finer  and  by  care  can  be  recovered  with- 
out chemical  loss."  (Dr.  Scheidel.) 

The  bullion  produced  by  the  cyanide  process  must 
necessarily  vary  according  to  the  grade  of  ore  treated 
and  care  taken  for  its  recovery  and  refining.  While 
one  party  will  recover  bullion  950  fine,  another  will 
have  750  fine  or  less.  This  case  is  important,  since  it 
may  be  more  expensive  in  the  end,  as  purchasers  of 
bullion  pay  for  its  assay  value,  and  refiners'  charges 
are  more  for  base  bullion  than  fine ;  under  such  con- 
ditions it  may  be  profitable  to  use  care.  Bullion  pre- 
cipitated by  zinc  has  objections  which,  although  at 
times  are  in  a  measure  unavoidable,  can  be  circum- 
vented to  some  extent  by  close  application  to  details. 
The  loss  of  bullion  from  smelting  is  one  of  the  most 
objectionable  features;  the  loss  of  zinc  does  not 
amount  to  much ;  the  loss  of  cyanide  is  a  bad 
feature,  but  unavoidable — we  expect,  however,  to  see 


CYANIDE   PROCESSES.  47 

this  reduced  and  the  process  carried  on  with  much  less 
cyanide  in  the  future. 

Practice  makes  perfect,  and  when  the  cost  has 
reached  as  low  as  $i  per  ton  the  method  is  becoming 
nearly  perfect.  We  also  expect  to  see  the  recovery 
very  much  simplified,  so  that  the  recovered  bullion  will 
be  finer  and  the  process  more  readily  accomplished. 

The  foundation  having  been  laid,  the  house  can  be 
completed. 


CHAPTER  VIII. 

THE  RECOVERY  BY  THE  CYANIDE  PROCESS. 

IF  by  amalgamation  of  a  $40  ore,  70  per  cent  has 
been  recovered,  it  is  considered  excellent  work;  if  now 
by  the  cyanide  process  and  use  of  $12  tailings  90  per 
cent  more  is  recovered,  we  can  consider  it  par  excel- 
lent work,  since  we  have  recovered  all  but  $1.20  in  the 
ore. 

The  Rand  Extraction  Company  of  South  Africa 
treats  tailings  averaging  5  dwt.  of  gold  to  the  ton 
equal  by  our  figures  to  $5  Per  ton.  They  recover  80 
percent  of  this,  or  $4  per  ton.  The  writer  has  known 
from  personal  observation  of  the  recovery  of  98  per 
cent  from  pure  quartz  carrying  gold,  and  of  another 
instance  of  97^  per  cent  from  clayey  ore,  while  on  the 
other  hand,  for  very  good  reasons,  but  20  per  cent  of 
the  fire-assay  value  was  recovered.  From  this  we 
deduce  that  the  character  of  the  ore  has  much  to  do 
with  the  percentage  recovered,  and  moreover  that  the 
cyanide  process  is  not  applicable  to  every  ore  contain- 
ing gold  and  silver. 

If  gold  can  be  extracted  economically  without  too 
great  loss  of  quicksilver,  amalgamation  should  precede 

48 


CYANIDE  PROCESSES.  49 

the  cyanide  process,  for  the  cost  will  be  very  small,  and 
we  can  almost  surely  count  on  the  recovery  of  90  per 
cent  of  the  gold  in  the  tailings  by  the  cyanide  process. 

Again,  as  before  mentioned,  it  requires  longer  time 
for  cyanide  to  absorb  coarse  gold,  than  it  does  mercury. 
These  remarks  apply  only  to  free-milling  gold  ores, 
and  not  to  refractory  or  tailings  ores,  but  it  is  in  this 
last  instance  we  appreciate  the  importance  of  the 
process  most.  Ores  charged  highly  with  metallic  sul- 
phides can  be  treated  as  before  stated,  but  ores  con- 
taining a  high  percentage  of  base  metals  cannot 
without  first  being  oxidized.  Ores  carrying  above  5 
per  cent  metal  are  smelting  ores ;  if  they  carry  that 
much  gold  they  are  bonanzas :  in  either  case  if  it  be 
possible  to  send  them  to  the  smelters,  unless  free- 
milling  gold  ores,  they  should  be. 

The  base  and  refractory  ores  generally  contain  such 
metals  as  iron,  zinc,  lead,  and  copper,  besides  such 
non-metal  substances  as  antimony,  bismuth,  arsenic  in 
the  form  of  sulphides,  arsenides,  antimonides,  etc. 

Cyanide  of  potassium  dissolves  metals  more  or  less, 
forming  generally  double  salts.  When  the  metals  are 
not  free,  but  are  chemically  combined  with  some  other 
substance,  such,  for  example,  as  sulphur,  forming  sul- 
phides, they  are  not  dissolved.  It  is  well  known  that 
the  affinity  of  cyanogen  for  the  precious  metals  is 
more  than  for  the  base  metals,  but  the  weaker  the 
solution  of  cyanogen,  is  the  less  likely  are  the  base 


50  CYANIDE  PROCESSES. 

metals  to  be  attacked.  The  only  sure  method  of  de- 
termining whether  the  process  is  suitable  for  an  ore 
is  by  laboratory  tests.  However,  it  is  stated  that  should 
ores  contain  hydrated  copper  oxides,  copper  carbon- 
ates, or  a  considerable  quantity  of  antimony,  arsenic, 
etc.,  the  cyanide  process  will  not  prove  satisfactory. 

Copper  compounds  physically  hard  are  not  acted 
upon,  but  when  soft,  porous,  and  open  the  action 
upon  them  decidedly  interferes  with  the  solution. 

Dr.  Scheidel  found  copper  carbonate  ore  which 
while  hard  gave  a  very  marked  reaction  on  cyanide 
solutions.  One  fourth  ounce  of  this  ore  shaken 
fifteen  minutes  with  2.73  per  cent  cyanide  of  potas- 
sium solution  reduced  the  strength  of  the  solution  to 
0.05  percent  cyanide.  "The  treatment  of  the  ore 
in  question,  notwithstanding  the  rapid  consumption 
of  the  cyanide,  showed  that  70  per  cent  of  the  gold 
was  extracted  from  the  ore,  while  no  silver  was  ex- 
tracted." 

We  would  naturally  expect  that  such  ores  would 
need  preliminary  treatment,  and  he  gave  it  one  with 
sulphuric  acid,  which  he  says  "  had  a  beneficial  effect 
on  the  consumption  of  cyanide,  and  thereby  on  the 
extraction  of  gold." 

.  MacArthur  says  ''that  cyanide  solution  acts  very 
slightly  on  antimonial  ores,  but  that  these  ores  hold 
gold  very  firmly,  and  as  the  compound  is  impervious, 
the  cyanide  is  unable  to  penetrate  the  mass  and  thus 


CYANIDE   PROCESSES.  5  I 

dissolve  the  precious  metal  from  the  base."  Both 
with  copper  and  antimony  cyanide  solutions  will  act 
upon  the  gold,  but  with  much  of  the  bases  present  the 
preliminary  treatment,  together  with  the  consumption 
of  cyanide,  will  probably  make  the  process  unprofitable. 
This,  however,  would  depend  upon  the  value  of  the  ore, 
as  some  ores  can  stand  considerable  expense  and  then 
pay. 

An  arsenical  ore  from  the  Mercur  lode,  Utah, 
carrying  20  per  cent  arsenic  was  treated  at  Denver. 
The  results  obtained  were  not  such  as  to  warrant  the 
tieatment  of  this  ore  by  the  cyanide  process.  On  the 
other  hand  an  arsenical  ore  from  Boulder,  Col. 
gave  an  extraction  of  79.4  per  cent,  and  still  another 
gave  an  extraction  of  82  per  cent,  at  a  treatment  cost 
of  $2.50  per  ton. 

Why  ores  of  the  same  class  will  not  both  yield 
readily  to  extraction  has  yet  to  be  ascertained  by  the 
aid  of  the  microscope  and  chemical  tests. 

The  percentages  of  recovery  depend  upon  so  many 
things  that  are  not  understood  that  we  can  only  say 
that  the  character  of  the  ore  is  the  chief  obstacle  to 
high  recovery. 

An  average  of  eight  concentrates  from  eight  dif- 
ferent mines  gave  a  recovery  of  88.13  per  cent.  The 
average  quantity  treated  was  12.38  tons,  and  its 
average  gold  value  per  ton  was  2  oz.  8  dwt.  1 1  grs. 

From  43.5  tons  of  tailings,  the  assay  value  of  which 


52  CYANIDE   PROCESSES, 

was  I  oz.  ii  dwt.  4  grs.,  89  per  cent  of  the  gold  was 
recovered. 

From  four  samples  of  ore  average  weight  1.875  tons 
each,  assaying  2  oz.  7  dwt.  5  grs.  gold  per  ton,  and  carry- 
ing 17  oz.  9  dwt.  1 8  grs.  silver  per  ton,  the  average 
recovered  was  87.21  per  cent  gold  and  62.19  Per  cent 
silver.  Highest  recovery  of  gold  91.09  per  cent; 
lowest  8 1. 1 8  per  cent.  Highest  recovery  of  silver 
79.78  per  cent ;  lowest  35.16  per  cent.  The  follow- 
ing table  gives  the  recovery  from  different  characters 
of  ore,  each  from  different  mines — G.  gold,  S.  silver : 

Per  cent.  Per  cent. 

Ironstone  and  kaolin G.  80. 3 

Lead  ore G.  88.7          S.  59.58 

Arsenical  pyrites G.  82 

Hematite G.  80  S.  61.55 

Silver  ore. S.  89.98 

Iron  pyrites   G.  98  S.  63 

Stephanite G.  90  S.  83.4 

Siliceous  ore G.  94  S.  82 

Mixed  tailings G.  80 

Quartz  and  talc G.  86 

Talcose G.  86 

Fifty  per  cent  sulphur  pyrites....  G.  92 

Oxidized  ore  with  limonite G.  93 

Sulphuretted  copper  ore G.  86 

Sulphur,  arsenic,  antimony G.  80 


CYANIDE  PROCESSES.  53 

Per  C2nt. 

Quartz  and  fine  gold G.  87 

Rusty  quartz G.  93 

Ore  kaolin G.   100 

Ore  quartz G.   100 

The  production  as  reported  for  five  years  from 
South  African  gold-fields  shows  the  recovery  on  a 
grand  scale.  The  process  was  applied  mostly  to  tail- 
ings, and  is  here  given  in  ounces:  1890,  286;  1891, 
34,862;  1892,  178,688;  1893,330,510;  1894,635,- 
900.  These  figures  are  deserving  of  more  than  an 
ordinary  glance,  since  they  represent  the  progress  made 
in  one  field  since  the  introduction  of  the  process  in 
1890;  but  especially  are  they  deserving  of  considera- 
tion when  they  are  known  to  represent  ounces  of 
gold  discarded,  thrown  away  as  of  no  use,  until  the 
introduction  of  the  process  made  their  recovery  pos- 
sible. While  it  is  not  exactly  in  accordance  with 
the  ideas  of  the  author  to  chronicle  the  cost  of  treat- 
ment, yet  one  comparison  may  not  be  amiss.  Mr. 
G.  S.  Peyton  of  the  Mercur  gold  mine,  Utah,  stated 
in  print  that  while  1500  tons  yielded  20  per  cent  of 
the  assay  value  of  his  ore  by  amalgamation  at  a  cost 
of  $4.25  per  ton,  1600  tons  treated  with  cyanide 
gave  an  extraction  of  88.5  per  cent  at  a  cost  of  $2.25 
per  ton. 


CHAPTER  IX. 

LABORATORY-WORK. 

HAVING  followed  the  process  from  the  stamps  to 
the  bullion,  we  can  now  turn  our  attention  to  the  tests 
necessary  to  be  made  to  intelligently  conduct  the  work. 
Our  first  inquiry  should  be,  How  shall  we  ascertain  the 
fitness  of  an  ore  for  cyanide  treatment?  We  must 
first  crush  our  samples, — the  finer  the  better, — and  pass 
part  of  them  through  a  sieve,  keeping  the  remainder 
or  coarser  part  for  duplicate  tests  if  they  are  needed. 

To  ascertain  if  the  ore  is  acid  and  needs  preliminary 
treatment,  take  400  grams  and  shake  it  with  water;  if 
the  water  turns  the  litmus  paper  from  blue  to  red,  there 
is  acid  present.  Add  now  lime,  a  little  at  a  time,  every 
now  and  then  shaking  until  the  litmus  paper  no  longer 
turns  red.  The  acid  in  the  ore  has  become  neutralized. 
Wash  this  ore  thoroughly  to  remove  any  traces  of 
lime.  The  ore  is  then  ready  for  cyanide  treatment. 

There  should  be  at  least  four  tests  made  of  100 
grams  each  of  ore. 

The  ore  is  placed  in  glass  bottles  with  solutions  of 

various  strengths. 

54 


CYANIDE   PROCESSES.  55 

These  are  shaken,  some  a  longer  time  than  others, 
the  time  varying,  the  object  being  to  ascertain  the 
amount  of  cyanide  consumed  by  the  ores  in  different 
times,  and  which  strength  is  best  suited  for  the 
standard  or  strong  solution,  as  well  as  the  time  neces- 
sary for  the  reaction. 

The  cyanide  consumed,  the  assay  of  the  ore  before 
treatment,  and  then  again  after  treatment  give  the 
required  data. 

These  tests  will  also  determine  whether  an  ore  is 
suitable  for  treatment  or  not  by  examination  of  the 
amount  of  cyanide  consumed.  Percolation  tests  can 
now  be  made  with  solutions  of  various  strengths  and 
various  lengths  of  time.  Analyses  now  made  of  the 
percolations  and  assays  of  the  well-washed  residues 
will  show  the  best  treatment  to  use.  These  small 
tests  are  excellent  guides  for  treatment  on  a  larger 
scale. 

Fire  assays  of  ore  to  be  treated  should  be  made  as 
the  first  step  to  ascertain  the  value  or  weight  of  the 
gold  per  ton ;  also  that  the  process  may  be  followed 
by  assay  to  see  how  the  cyanide  is  dissolving  the 
gold.  We  must  also  measure  our  cyanide  by  this 
assay.  We  have  seen  that  theoretically  I  part  of  cya- 
nid.e  will  dissolve  1.5  parts  of  gold,  but  that  practically 
we  need  from  3  to  4  pounds  of  cyanide  for  I  ounce 
of  gold ;  the  amount  actually  necessary  therefore  can 
only  be  determined  by  the  shaking  and  percolating 


56  CYANIDE   PROCESSES. 

laboratory  tests.  One  object  is  to  be  borne  in  mind 
while  making  these  tests:  that  it  is  not  how  much,  but 
how  little,  cyanide  can  be  used  and  yet  extract  all  the 
gold. 

To  determine  the  gold  and  silver  in  a  solution  of 
cyanide  of  potassium :  Take  a  known  quantity  of 
the  liquor  and  precipitate  the  silver  with  a  solution 
of  sodium  sulphide  or  iron  sulphide.  Filter  off  the 
remaining  liquor,  dry,  and  wrap  the  precipitate  in 
sheet-lead  with  a  little  granular  lead  and  cupel. 
The  remaining  solution  containing  the  gold  is  treated 
with  chloride  of  zinc,  which  precipitates  the  gold. 
This  is  then  dried,  mixed  with  granular  lead,  and 
cupelled. 

If  there  has  been  an  excess  of  cyanide  solution 
used,  there  will  be  a  waste  of  cyanogen  in  treating  the 
mass  of  ore. 

To  ascertain  the  strength  of  the  cyanide  solution : 
Take  a  burette  and  pour  into  it  a  solution  of  nitrate 
of  silver,  AgNO3,  whose  strength  for  I  c.c.  will  equal 
the  strength  of  o.  I  gram  potassium  cyanide  used. 
Take  a  known  quantity,  10,  20,  or  50  c.c.,  of  the 
cyanide  solution  being  used,  and  drop  into  it  the 
silver  nitrate,  shaking  the  cyanide  to  mix  the  two 
solutions.  After  a  time  the  cyanide  solution  shows 
slight  turbidity;  when  it  shows  distinct  turbidity, 
stop,  and  read  the  burette.  For  example,  if  20  c.c. 
cyanide  solution  titrated  by  1.15  c.c.  of  the  stand- 


CYANIDE   PROCESSES.  57 

ard  AgNO3  solution,  the  strength  of  the  cyanide 
solution  would  be  found  by  dividing  1.15  by  20  = 
0.057  Per  cent. 

Mr.  J.  E.  Clennell  made  some  investigations 
which  were  published  in  the  Chemical  News,  and 
again  in  the  Engineering  and  Mining  Journal.  Ex- 
tracts are  given  from  his  investigations : 

1.  Solutions   of   cyanide    are   frequently   met    con- 
taining such  fine  matter   in    suspension  they    cannot 
be  filtered  clear.      If  to  such  solutions  lime  and  agita- 
tion be  applied,  they  can  be  filtered  clear. 

When  soluble  double  cyanides  were  present,  this  was 
inaccurate,  but  if  only  finely  divided  inert  substance 
was  in  suspension  it  was  practically  correct. 

With  double  salts  such  as  are  obtained  from  zinc 
filter-boxes  the  reactions  made  by  lime  are  incom- 
plete, hence  valueless.  Thus : 

K,ZnCy,  +  Ca(OH),  -  Zn(OH)2  +  K,Cy,  +  CaCy,  . 

2.  Turbid  solutions  free  form  zinc  can  be  titrated 
without  filtering  by  Fordo's  and  Gelis'  method.     The 
process  depends  upon  the  considerations : 

a.  That  a  mixture  containing  alkaline  cyanides, 
hydrates,  and  monocarbonates  has  the  hydrates  con- 
verted into  neutral  salts,  and  the  monocarbonates 
into  bicarbonates,  by  addition  of  dilute  mineral  acid, 
before  any  of  the  cyanides  are  decomposed. 


58  CYANIDE   PROCESSES. 

b.  That  bicarbcmates   of  the  alkali  metals  do   not 
act  on  iodine. 

c.  When     cyanide    in    such   a    mixture    has     been 
converted    into   a    double    silver    salt,    titration    with 
dilute    hydrochloric    acid,    with     phenolphthalein    as 
indicator,    shows  the   quantity  required   to   neutralize 
the  hydrates  and  convert   the  carbonates  into  bicar- 
bonates. 

Iodine  Process. — a.  A  solution  of  iodide  of  potas- 
sium is  standardized  against  a  solution  of  pure  po- 
tassium cyanide,  the  strength  of  which  has  been 
determined  by  the  silver  nitrate  method.  The  end 
point  of  the  iodine  reaction  is  marked  by  a  permanent 
yellow  tint,  or  if  starch  be  added  by  a  bluish-yellow 
color,  and  is  in  general  sharp  and  delicate. 

It  is  essential,  however,  that  the  solution  shall 
contain  no  free  caustic  alkali  or  alkaline  monocar- 
bonate,  as  these  bodies  react  with  iodine,  rendering 
the  indications  too  high  and  indefinite. 

b.  Silver  nitrate  is  added  to  a  measured  volume  of 
the  solution  to  be  tested  until  a  permanent  turbidity 
results,  or  if  the  solution  was  turbid  to  commence 
with  until  a  distinct  increase  is  observed.  A  drop  of 
phenolphthalein  indicator  is  now  added  to  the  same 
liquid  and  titration  is  continued  with  N/io  HC1  until 
the  pink  color  disappears.  Another  measured  por- 
tion of  the  original  solution  is  now  taken,  and  a  trifle 
less  hydrochloric  acid  than  was  necessary  to  neutralize 


CYANIDE   PROCESSES.  59 

the  alkali  in  the  preceding  experiment  is  added  drop 
by  drop  with  agitation.  The  solution  is  now  ready 
for  titration  with  iodine. 

The  following  experiments  illustrate  neutralizing 
the  alkali  by  hydrochloric  acid : 

Pure  cyanide  and  caustic  potash  were  mixed  so 
that  10  c.c.  of  the  mixture  required  3.7  c.c.  of  stand- 
ard iodine,  and  a  like  amount  required  1.15  c.c.  of 
standard  silver  nitrate. 

On  adding  phenolphthalein  and  titrating  with 
N/io  HC1  acid  5.75  c.c.  were  required.  10  c.c.  were 
then  mixed  with  5  c.c.  of  N/io  HC1  and  the  mixture 
titrated  with  iodine;  3.3  c.c.  were  required. 

Next  10  c.c.  were  mixed  with  5  c.c.  of  N/io  HC1 
and  the  mixture  titrated  with  standard  AgNO3; 
1.15  c.c.  were  required. 

In  these  experiments 

i  c.c.  standard  AgNO3  =  o.oi  gram  KCy; 
I  c.c.        •"         iodine    =0.0035. 

To  show  that  these  are  practically  correct  we  will 
calculate  them. 

1st.   3.7  c.c.  X  0.0035  =  °-I295  percent. 

2d.    1.15  X  o.oi       =  0.1150    "      " 

3d.    3.3  X  0.0035  =  0.1155    "      " 

4th.  1.15  X  o.oi       =  0.1150    "      " 

The  difference  between  one    and  three   shows  the 


60  CYANIDE   PROCESSES. 

advantage  of  neutralizing  the  hydrate  with  acid,  while 
the  difference  between  two  and  four  shows  no  variation 
when  silver  nitrate  is  used. 

When  an  impure  solution  of  cyanide  and  caustic 
were  used,  the  advantage  to  be  gained  by  the  use  of 
acid  was  in  favor  of  iodine,  a  trifle. 

A  mixture  of  cyanide  and  carbonate  gave  with 
silver  nitrate  0.044  KCy;  with  silver  nitrate  and  acid 
the  same  result — 0.044  KCy.  With  iodine  the  indi- 
cated strength  was  0.047  KCy. 

The  next  experiments  were  made  with  solutions 
containing  zinc,  but  satisfactory  results  were  not 
obtained. 

3.  Precipitation  by  Akaline  Sulphides. — a.  Zinc, 
silver,  or  mercury  existing  as  double  cyanides  are 
precipitated  by  sulphuretted  hydrogen  or  an  alkaline 
sulphide,  as  metal  sulphides. 

b.  The  excess  of  sulphides  may  be  removed  from 
the  cyanide  solution  without  affecting  the  cyanide  by 
addition  of  insoluble  compounds  of  lead,  such  as 
oxides,  carbonates,  etc. 

The  method  to  be  followed  is: 

First.  Measure  a  volume  to  be  tested ;  add  caustic 
potash  or  soda  until  the  cyanide  solution  is  strongly 
alkaline. 

Secondly.  Pass  into  the  now  alkaline  solution  H3S 
until  precipitation  ceases,  or,  what  is  better,  a  concen- 
trated solution  of  pure  sodium  sulphide.  Shake  the 


CYANIDE   PROCESSES.  6 1 

solution  well  and  allow  the  precipitate  to  subside. 
The  clear  solution  after  filtering  can  be  freed  from 
excess  of  sulphide  by  agitation  with  litharge  added 
little  by  little,  until  a  drop  of  the  liquor  no  longer 
gives  the  slightest  coloration  with  a  drop  of  lead 
acetate  solution.  A  definite  volume  is  now  filtered 
off  and  tested  with  silver  nitrate. 

The  liquid  to  be  tested  must  give  a  perfectly  white 
precipitate  with  a  drop  of  lead  acetate.  Also  it 
should  give  no  precipitate  with  sodium  carbonate, 
and  moreover  it  should  give  no  precipitate  with  sul- 
phuretted hydrogen. 

In  titrating  with  silver  nitrate  the  point  to  be 
noted  is  the  appearance  of  a  distinct  permanent  tur- 
bidity pervading  the  liquid  and  not  disappearing  on 
standing. 

Deductions  made  were,  that  wherever  a  quantity  of 
zinc  was  present  it  was  necessary : 

First.  To  remove  the  precipitation  by  filtration 
before  adding  lead  salts,  since  the  precipitated  zinc 
sulphide,  although  washed,  will  react  upon  car- 
bonate of  lead  with  formation  of  lead  sulphides ; 

Second.  A  solution  of  lead  acetate  is  liable  to  pre- 
cipitate cyanide  of  lead ;  hence  an  insoluble  com- 
pound of  lead  should  be  added  to  the  solution ; 

Third.  To  avoid  the  liberation  of  hydrocyanic  acid 
considerable  alkaline  hydrate  should  be  added  before 
precipitating  with  hydrogen  sulphide ; 


62  CYANIDE  PROCESSES. 

Fourth.  Results  obtained  with  alkaline  monocar- 
bonates  were  not  satisfactory. 

The  following  experiments  will  illustrate  the  ap- 
plication of  the  method : 

Suppose  we  take  100  c.c.  of  the,  liquid  from  what 
has  passed  through  the  zinc-boxes,  and  which  con- 
tains K2Cy4Zn. 

We  make  this  strongly  alkaline  by  addition  of  con- 
centrated caustic  soda,  and  by  addition  of  hydrogen 
sulphide  precipitate  sodium  and  zinc  sulphide. 

This  liquor  is  then  filtered,  and,  if  necessary,  a  little 
lime  is  added  to  make  the  filtrate  clear. 

This  filtrate  is  now  shaken  with  an  insoluble  lead 
compound,  such  as  litharge  or  lead  carbonate,  and 
25  c.c.  are  now  filtered  off. 

Supposing  our  pure  potassium  cyanide  is  I  c.c. 
=  0.231  KCy,  and  that  i  c.c.  of  zinc  sulphate  =  0.02 
gram  Zn.  Then  in  the  double  cyanide  K2ZnCy4 
I  c.c.  =  0.08,  and  the  free  potassium  cyanide  —  0.231 
—  0.08  =  0.151  KCy. 

On  titrating  with  AgNO3  we  find  it  requires  from 
our  burette  readings  5.7  c.c.  AgNO3  for  distinct 
turbidity. 

5.7-1-25  =  .228  per  cent  KCy ;  but  four  times  this 
gives  total  cyanide  or  0.912  per  cent  KCy  as  the 
indicated  strength  of  the  solution. 


CYANIDE  PROCESSES,  63 

GENERAL   INFORMATION. 

Briefly,  the  cyanide  process,  leaving  out  the  mechan- 
ical arrangements  for  doing  the  work,  is  conducted 
as  follows : 

The  ore  after  reaching  the  mill  is  crushed,  rolled, 
and  stamped.  If  amalgamation  is  practised,  it  takes 
place  during  the  stamping.  If  wet  crushing  is  em- 
ployed, three  to  five  gallons  of  water  per  minute  will 
be  required.  The  tailings  from  the  stamps  are  con- 
veyed directly  into  vats  by  means  of  launders. 

The  vats  may  be  made  of  iron,  coated  with  tar  or 
asphalt ;  or  of  brick,  lined  with  hydraulic  cement ;  or 
of  wood  coated  with  asphalt  or  lined  with  cement. 

Each  vat,  if  the  MacArthur-Forrest  process  is  be- 
ing used,  should  be  large  enough  to  hold  one  day's 
run  from  the  stamp-mills.  These  vats  are  made  of 
enormous  size,  at  times  fifty  feet  in  diameter,  capable 
of  holding  five  hundred  tons  of  ore  and  solution. 

Wherever  possible,  the  plant  should  be  so  arranged 
that  advantage  may  be  taken  of  gravity,  as  this  will 
obviate  the  use  of  elevating  machinery  and  much 
pumping.  The  leaching-tank,  or  the  first  vat  of  the 
series  which  holds  the  ore  and  solution,  should  have  a 
capacity  of  twice  the  second  tank  of  the  series,  which 
holds  only  the  gold  in  solution. 

The  tank  next  in  order  is  the  precipitating-vat  or, 
as  it  is  termed,  the  zinc-box,  and  this  should  have 


64  CYANIDE  PROCESSES. 

compartments  enough  to  allow  the  precipitation  of  all 
the  gold  from  the  solution. 

Following  the  precipitating-boxes  are  the  sumps, 
which  receive  the  weak  liquor  from  them,  and  should 
be  of  such  size  as  to  hold  the  solution  from  two 
teachings. 

There  is  still  another  tank  called  the  stock-tank 
which  contains  a  strong  solution  of  potassium  cyanide, 
and  there  should  be  yet  another  to  which  the  weak 
liquor  from  the  sump  may  be  pumped  and  brought 
up  to  the  standard  or  strong  solution  by  additions 
from  the  stock-tank.  The  sump  solutions  are  used 
over  and  over  again  by  making  up  from  the  stock-tank 
the  loss  of  cyanide  which  took  place  during  the  former 
operations,  or  they  may  be  used  as  weak  solutions 
at  the  commencement  of  the  operation  or  as  wash  at 
the  finish.  In  any  case  by  using  the  sump  liquor 
cyanide  is  saved. 

The  cost  of  cyanide  98  per  cent  pure  is  fifty  cents 
per  pound  in  New  York  City.  It  is  costly  and  worth 
economizing.  Since  the  process  has  increased  the 
demand  for  cyanide  of  potassium,  it  is  of  importance 
to  buy  it  from  some  firm  which  can  be  relied  upon, 
and  which  tests  it  occasionally  to  ascertain  its 
strength.  The  tendency,  as  the  subject  has  been 
practically  worked,  is  to  greatly  reduce  the  amount  of 
cyanide  used ;  where  it  was  formerly  customary  to  use 
\\  and  more  per  cent  of  cyanide  in  the  solution,  now 


CYANIDE  PROCESSES.  65 

equally  good  results  are  obtained  from  the  same  ore 
by  1/2  per  cent  for  the  strong  solutions  and  3/10  per 
cent  for  the  weak  solutions. 

Of  course  the  ore  and  gold  to  be  dissolved  will 
have  an  influence  upon  the  strength  of  the  solution, 
also  the  silver,  but  the  object  of  the  operator  should 
be  to  keep  the  solution  as  low  as  consistent  with  the 
work  in  hand,  bearing  in  mind  that  the  weaker  the 
solution  the  less  likely  it  will  be  to  attack  any  base 
metals  present,  and  the  less  loss  will  occur  from  oxi- 
dation and  in  the  zinc-precipitation  boxes.  In  this 
latter  instance  the  greatest  loss  takes  place,  and  for 
that  reason  inventors  have  endeavored  to  find  some 
better  method  of  precipitation.  Some  establishments 
instead  of  allowing  the  solution  to  go  through  the 
precipitation-boxes  pump  it  back  on  to  the  ore  or  use 
it  upon  ore  in  another  vat,  thus  making  two  or  more 
treatments  with  the  gold  in  cyanide  solution  before 
precipitating  the  gold  by  zinc,  thus  economizing  in 
the  use  of  cyanide  by  this  means  and  saving  zinc  as 
well.  This  method,  we  are  informed,  is  carried  on  at 
the  Robinson  works  in  South  Africa,  with  extraction 
results  equalling  the  former  practice. 

The  numerous  methods  being  devised  for  saving 
cyanide  and  lessening  the  cost  of  the  process,  to- 
gether with  the  numerous  patents  being  issued, 
must  impress  the  thoughtful  man,  no  matter  how 


66  CYANIDE  PROCESSES. 

prejudiced  he  may  be,  that  there  must  be  some  merit 
in  the  process  worthy  consideration. 

It  is  not  claimed  by  any  one  we  are  aware  of  that 
all  ores  can  be  treated  successfully,  for  such  is  not  the 
case,  but  we  believe  that  it  can  treat  any  ore  where  as 
much  care  is  taken  with  oxidation  as  in  other  proc- 
esses with  equally  good  results  and  cheaper. 

There  may  be  given  as  one  reason  why  better  re- 
sults have  not  been  obtained  in  the  treatment  of  tail- 
ings that  amalgam  on  the  surface  of  gold  protects  it 
to  an  enormous  extent  from  the  solvent  action  of 
potassium  cyanide. 

Another  reason  for  bad  results  may  be  given,  that 
not  enough  oxygen  from  the  air  was  allowed  to  come 
in  direct  contact  with  the  ore  and  solution. 

The  poor  results  obtained  in  the  treatment  of  con- 
centrates may  be  obviated  by  allowing  more  time  for 
the  cyanide  solution  to  act  upon  them,  or  by  finer 
pulverization.  In  both  cases  the  action  of  the  cyanide 
solution  can  be  hastened  by  agitation. 

In  regard  to  the  necessity  of  oxygen  for  hastening 
and  carrying  on  the  operation  Mr.  F.  A.  Mason  de- 
duced the  following  from  some  recent  experiments: 

First.  That  by  passing  air  through  solutions  of 
potassium  cyanide  the  solubility  of  gold  was  increased. 
This  will  be  the  subject  of  several  more  patents. 

Second.  That  air  when  forced  against  a  plate  of 
gold  in  a  cyanide  solution  causes  it  to  dissolve  with 


CYANIDE   PROCESSES.  6? 

more  rapidity  in  that  solution.  This  again  proves  the 
truth  of  Eisner's  equation. 

Third.  That  amalgam  on  the  surface  of  gold, 
even  when  air  is  forced  against  it,  protects  the  gold 
from  the  action  of  potassium  cyanide.  This  experi- 
ment shows  the  weak  action  of  cyanide  upon  mercury. 

Ore-sampling. — The  probabilities  are  that  lean  ores 
will  afford  the  greater  bulk  of  the  ores  treated  by 
chemical  processes,  because  they  will  not  bear  the 
transportation,- sampling,  freight,  and  other  charges 
to  the  smelters. 

In  some  instances,  however,  when  the  smelters  may 
need  "  silica"  for  a  flux  so  badly  as  to  use  pebbles, 
they  will  agree  to  stand  one  half  the  expenses,  or  even 
buy  the  ore ;  but  such  instances  are  likely  to  prove 
rare,  as  the  smelters  can  afford  such  buying  only  in 
extreme  cases,  and  even  then  only  to  a  limited  ex- 
tent, depending  upon  the  distance  and  freight  charges 
from  the  mines  to  the  smelters. 

The  smelters  being  generally  situated  in  a  locality 
suitable  for  obtaining  different  classes  of  ores,  and 
nearer  fluxes  and  coal  on  which  they  pay  freight  than 
the  ore  on  which  the  miners  pay  freight,  their  useful- 
ness for  low-grade  ores  is  a  question,  unless  the  con- 
centrates of  such  ores  are  shipped  them.  Were  the 
smelters  compelled  to  treat  all  low-grade  .ores,  there 
would  be  very  few  smelters,  as  then  the  actual  run- 
ning expenses  would  either  bankrupt  the  smelters  or 


68  CYANIDE   PROCESSES. 

their  charges  would  prohibit  the  miners  shipping  their 
ore.  In  any  case  the  smelter  is  more  useful  for  high- 
grade  ores  too  rich  for  treatment  at  the  mines,  and 
for  this  purpose  they  are  a  necessity;  while  those 
ores,  on  the  other  hand,  which  can  be  treated  at  the 
mines  by  the  chemical  processes  and  yield  good  re- 
turns will  not  go  to  the  furnaces.  In  both  cases 
where  the  works  are  public,  that  is,  buy  the  ore  for 
treatment  from  the  miners,  the  public  sampling-mill 
is  agent  virtually  for  miner,  and  smelter,  or  reduction- 
works. 

On  the  returns  from  the  assays  made  by  the 
sampling-mill  the  ore  is  paid  for.  The  ore  is  not 
shipped  direct  to  the  smelter,  but  to  the  sampling- 
works.  Here  it  is  unloaded  from  the  car  and  weighed. 
It  is  then  run  through  crushers;  from  the  crushers  it 
passes  through  rolls ;  from  the  rolls  it  is  elevated  and 
comes  down  by  gravity  through  a  pipe  which  auto- 
matically samples  it,  by  quartering  it  as  it  falls,  and 
finally,  after  this  mixing,  receives  one  quarter  in  a 
separate  bin,  while  the  three  quarters  are  removed  to 
the  dumping-bin. 

After  the  car-load  of  ore  has  been  sampled  auto- 
matically in  this  way  it  would  appear  to  be  as  accu- 
rately accomplished  as  any  hand-work  could  possibly 
do  it.  But  all  the  ore  is  not  of  the  same  value;  hence 
the  mixing  of  this  sample  must  be  attended  to. 

It  is  now  removed  from  the  bin  and  shovelled  in  a 


CYANIDE    PROCESSES.  69 

cone-shaped  pile  on  the  floor,  the  ore  always  running 
off  the  end  of  the  shovel  to  the  apex  of  the  cone,  so 
as  to  run  as  evenly  as  may  be  down  the  sides  of  the 
cone.  Throwing  a  shovelful  of  ore  on  the  apex  of  the 
cone  will  not  accomplish  this  result,  but  easy  handling, 
as  mentioned,  will.  This  operation  is  done  once  or 
twice  more,  after  which  cutting  down  the  sample  is 
commenced. 

To  accomplish  the  cutting  down  the  pile  called  the 
sample  is  shovelled  from  the  floor  on  a  sampling- 
shovel,  which  is  made  to  catch  about  half  of  the  ore 
from  the  floor,  the  remainder  falling  into  a  barrow. 
This  sample  thus  reduced  goes  into  three  separate 
buckets,  first  one,  then  another,  and  finally  the  third, 
when  the  rotation  is  commenced  over  again.  The 
original  sample  is  now  cut  down  one  half,  but  is  still 
very  much  too  large,  so  that  the  ore  from  the  three 
tubs  is  coned  again  on  the  floor  as  in  the  first  place, 
and  again  cut  down  one  half  in  quantity. 

It  is  now  run  through  the  crushers  and  sifted,  and 
again  cut  down,  but  before  this  cutting  down  all  that 
did  not  pass  through  the  sieve  is  crushed  until  it  does. 
These  three  samples  will  now  weigh  about  one  hun- 
dred pounds  each  or  less.  This  is  too  much,  so  they 
are  still  further  mixed  until  reduced  to  ten  pounds 
or  less,  when  they  are  pulverized  to  pass  through 
a  loo-mesh  screen.  Then  one  part  of  each  is  sent 
to  the  assayer.  Should  there  be  much  variation  in 


70  CYANIDE   PROCESSES. 

the  assay  returns,  the  operation  of  sampling  is  re- 
peated when,  if  the  assays  tally  closely,  the  average 
is  taken  as  a  basis  for  settlement. 

It  is  well  to  remark  that  various  ores  contain  more 
or  less  moisture,  so  that  a  lot  of  say  100  pounds 
is  weighed,  then  dried,  and  weighed  again.  The 
total  wreight  is  now  reduced  just  that  much,  for  if  a 
lot  of  100  pounds  contains  2  per  cent  moisture,  a  car- 
load of  10,000  pounds  will  contain  200  pounds,  and 
the  smelter  objects  to  paying  for  that  much  water. 
After  the  assay  has  proved  satisfactory  to  all  con- 
cerned the  sampler  settles  with  the  miner  but  first 
deducts  his  charges  for  sampling  with  the  smelter's 
charges,  and  the  sampler  in  turn  settles  with  the 
smelter. 

The  sampling- works  have  become  almost  a  necessity, 
as  the  miner  feels  better  satisfied  with  his  returns,  and 
the  smelter  is  satisfied  because  he  is  not  accused  of 
fraud.  Whether  the  samplers  are  satisfied  we  are  not 
sure,  but  presume  they  are,  since  public  sampling  is 
now  carried  on  in  every  camp  of  size. 

There  are  many  cases  where  the  miner  cannot  afford 
to  loose  the  time  and  be  to  the  expense  of  following 
his  ore  to  the  sampler;  he  therefore  hires  an  agent 
who  attends  to  the  sampling.  This  man  is  called  the 
miner's  agent;  he  checks  the  weights,  the  moisture, 
and  watches  the  sampling. 

The  sampler's  scales  are  regularly  tested  by  the  pub- 


CYANIDE   PROCESSES.  /I 

lie  scale  inspector,  so  that  every  possible  safeguard  is 
afforded  the  miner  against  loss  of  values.  He  can, 
however,  if  he  wishes  sample  his  ore  and  have  his 
assay  made  before  shipping,  but  we  consider  it 
doubtful  if  he  did  not  employ  the  sampler  whether 
he  could  have  settlements  with  the  smelter  on 
his  returns  if  they  differed  much  from  the  smelter's 
assay.  The  ore  to  be  sampled  at  the  mines  is  first 
broken  by  passing  it  through  a  crusher.  From  the 
crushed  ore  every  fifth  shovel  is  reserved  for  sample, 
the  remainder  being  carried  into  the  railroad  car  for 
shipment.  This  sample  is  now  crushed  finer  by  pass- 
ing it  through  the  rolls ;  it  is  then  coned  on  the  floor 
as  above,  flattened  out,  and  divided  into  four  parts, 
the  two  opposite  being  saved  as  the  sample,  while  the 
remainder  is  taken  into  the  car.  This  is  again  coned 
and  quartered  until  the  sample  is  much  reduced  in 
size,  say  to  one  hundred  pounds.  It  is  then  weighed, 
afterwards  heated  to  drive  off  the  moisture,  and 
crushed  to  go  through  a  very  fine  sieve,  after  which  it 
is  reduced  to  size  necessary  for  assay  by  the  same 
method.  This  at  times  gives  very  accurate  results, 
and  is  a  check  upon  agent,  sampler,  and  smelter. 


CHAPTER  X. 

GOLD    AND    SILVER    SOLVENTS    COMBINED    WITH 
ELECTRICAL  ACTION. 

ACCORDING  to  Berzelius,  "  Chemical  union  of  any 
two  substances  is  an  electrical  act ;  that  during  contact 
previous  to  union  the  one  substance  is  relatively  posi- 
tive, the  other  relatively  negative,  and  the  act  of 
union  is  a  consequence  of  the  attraction  existing  be- 
tween the  substances  in  these  two  states;  also  that  in 
the  act  of  uniting  the  two  electrical  conditions  neutral- 
ize each  other  and  produce  heat." 

Professor  Bunsen  used  to  say  that  electrolysis  in  all 
operations  marks  a  great  advance  on  chemical  action 
pure  and  simple. 

As  MacArthur  and  Forrest  were  the  parties  to  intro- 
duce the  practical  application  of  cyanide  to  extraction 
of  gold  from  ores,  Siemens- Halske  may  be  considered 
the  first  to  introduce  electricity  into  the  process  to 
assist  its  application.  Neither  of  them  designed  or 
produced  anything  new,  but,  having  strength  in  their 
convictions,  they  applied  their  patents  to  obtain  useful 

results. 

72 


CYANIDE  PROCESSES.  73 

A  good  thing  laying  dormant  is  of  no  use  to  man- 
kind. 

When  Dr.  Siemens  took  the  matter  up,  he  found 
that  electrical  precipitation  was  equally  effective  with 
either  strong  or  weak  solutions  of  cyanide.  This  was 
one  step  in  the  right  direction,  namely,  a  saving  in 
chemicals. 

Julian  Rae  of  Syracuse,  N.  Y.,  patented  an  appara- 
tus as  early  as  1867  for  the  electrical  precipitation  of 
gold  from  ores,  but  the  patent,  like  Simpson's,  of 
1885,  seems  to  have  been  left  on  the  shelf  to 
mould.  Mr.  Rae  did,  however,  make  one  practical 
test,  which  was  not  entirely  satisfactory,  at  the 
Douglas  mill,  Nevada.  His  failure  to  obtain  uniform 
results  was  due,  we  believe,  to  his  using  an  alternating 
current.  Electrolysis  with  such  currents  must  neces- 
sarily be  very  slow,  and  the  slower  the  reversal  of 
the  current  the  better  the  results,  for  if  the  current 
alternates  quickly  there  will  not  be  given  time  for 
the  solution  to  deposit  its  metal  compound  before 
it  is  repelled  by  a  reversal  of  the  current. 

The  essential  conditions  necessary  for  electrolysis 
are  that  the  substance  be  a  liquid,  a  definite  chemical 
liquid,  and  a  conductor  of  electricity. 

Potassium  cyanide  with  gold  in  solution  answers 
these  conditions. 

When  potassium  cyanide  delivers  up  its  gold  to  the 
zinc  in  the  zinc-precipitation  boxes,  it  would  have  its 


74  CYANIDE   PROCESSES. 

potassium  immediately  converted  into  potash  by  oxy- 
gen did  not  potassium  cyanide  have  a  definite  chemi- 
cal composition  of  its  own  so  that  it  could  unite  with 
zinc  quickly.  The  zinc,  being  the  substance  liberated, 
unites  with  the  potassium  cyanide  to  form  zinc  potas- 
sium cyanide,  and  is  a  secondary  product  of  elec- 
trolysis. 

Not  only  precise  quantities  of  current,  but  definite 
amounts  of  electrical  energy,  are  required  to  decom- 
pose or  separate  weights  of  substances.  The  amount 
of  electrical  energy  required  to  separate  from  a  com- 
pound a  given  weight  of  metal  depends  upon  the 
strength  of  the  chemical  union,  the  chemical  equiva- 
lent of  the  substance  to  be  separated,  and  upon  the 
amount  of  the  conduction  resistance  of  the  electrolyte. 

The  question  of  a  cyanide  solution  being  increased 
in  dissolving  power  by  becoming  an  electrolyte  is  not 
quite  clear  to  the  writer.  That  gold  is  positive  there 
can  be  no  doubt,  and  that  cyanide  of  potassium  is 
negative  as  an  electrolyte  there  can  be  no  doubt ; 
but  we  are  told  that  the  solving  action  takes  place  at 
the  anode ;  hence  the  gold  positive  dissolves  to  the 
cyanide  solution  negative,  with  the  result  that  the 
gold  cyanide  solution  is  positive.  The  gold  is  able 
to  keep  its  electro-positive  condition  if  not  its  chem- 
ical condition. 

Whether  this  electrolyte  becomes  converted  into  an 
electrode  by  absorbing  the  gold  we  are  unable  to  say, 


CYANIDE    PROCESSES.  75 

but  when  they  become  "cations"  the  gold  is  in  the 
metallic  state  and  the  potassium  cyanide  is  immediately 
set  free.  The  potassium  also  should  be  set  free,  form- 
ing caustic  potash,  but  if  it  be  set  free  the  majority  of 
it  reunites  with  hydrocyanic  acid,  forming  potassium 
cyanide,  to  go  on  another  round  as  a  negative  electro- 
lyte to  collect  more  gold.  Of  this  much  we  are 
confident,  but  how  the  electric  current  stimulates  the 
solution  we  are  unable  to  comprehend. 

That  some  potash  is  set  free  at  the  cathode  we  are 
sure,  but  the  majority  is  reconverted  into  potassium 
cyanide. 

As  the  chief  amount  of  conduction  resistance  is  in 
the  electrolyte,  and  not  in  the  electrodes,  and  by  rise 
of  temperature  the  resistance  of  the  liquid  is  de- 
creased, the  effect  is  to  facilitate  electrolysis.  At 
the  same  time  this  rise  in  temperature  should  increase 
the  solubility  of  the  solution. 

The  electro-chemical  equivalents  of  gold  and  po- 
tassium cyanide  are  nearly  equal.  The  equivalent 
weights  are:  gold  65.4,  KCy  65. 

The  quantities  in  fractions  of  a  gram  separated  by 
one  coulomb  of  current  are:  gold  .000678,  KCy 
.000684.  Grams  separated  per  ampere  per  hour:  gold 
2.5128,  KCy  2.4624.  The  amount  of  electrical 
energy,  therefore,  required  to  separate  these  sub- 
stances being  about  equal  for  each  on  account  of 
nearly  equal  atomic  weights,  we  naturally  conclude  it 


?  CYANIDE   PROCESSES. 

is  small,  and  that  an  increase  of  current  past  a  certain 
point  would  be  a  waste  of  power. 

The  object  of  the  electric  current,  then,  as  we 
understand  so  far,  is  to  decompose  a  solution  of 
metallic  salt,  depositing  the  metal  upon  the  cathode 
or  negative  pole,  while  the  metal  is  dissolved  at  the 
positive  pole. 

If  we  use  an  iron  anode  with  sulphuric  acid,  we 
find  gold  is  electro-negative  to  iron,  while  if  we  use 
the  same  anode  in  potassium  cyanide,  gold  is  electro- 
positive to  iron. 

If  electro-positive  and  electro-negative  metals  be 
connected,  as  in  the  case  of  our  gold  cyanide  solution, 
they  form  a  galvanic  battery  of  their  own,  and,  being 
nearly  of  the  same  electro-chemical  relation,  it  ap- 
proaches perfection.  Were  there  any  data  to  go  by, 
we  could  almost  say  that  this  was  the  reason  why 
potassium  cyanide  had  such  an  affinity  for  gold. 

We  are  not  sure  that  these  little  galvanic  batteries 
have  any  action  whatever  on  the  results  of  the  other 
particles  of  gold  and  cyanide  uniting,  or  that  they  are 
a  means  of  conduction  between  the  electrodes,  since 
there  are  so  few  of  them  in  solution,  becoming 
gradually  less  as  deposition  at  the  cathode  takes 
place. 

In  a  fixed  time  a  given  electric  current  will  deposit 
a  certain  amount  of  metal,  which  will  vary  for  dif- 
ferent metals  in  direct  proportion  to  their  chemical 


CYANIDE   PROCESSES.  77 

equivalents.  One  coulomb  or  unit  of  quantity  of 
electrical  current  will  set  free  0.0.00162  grams  of  hy- 
drogen. Equal  weights  of  different  metals  in  dis- 
solving will  yield  unequal  amounts  of  current.  If, 
however,  the  metals  are  considered  in  proportion  to 
their  different  weights,  a  very  different  relation  is 
seen.  One  gold  coulomb  is  obtained  by 

0.000162  X  196.2 

-  —  o. 01061 1  gram  of  gold. 

One  silver  coulomb  is  obtained  by 

0.000162  X  107.7  —  0.01725  gram  of  silver. 

One  potassium  cyanide  coulomb  would  be  .010530. 
The  rate  of  deposition  of  these  various  substances,  or 
rather  their  dissolution  at  the  cathodes,  would  be  in 
one  hour  by  one  ampere  of  current 

0.01061 1  X  3600  —  38. 19  grains  gold ; 
0.01725     X  3600  .—  72.28      "      silver; 
0.01053    X  3600  =37. 90      "      KCy. 

To  deposit  one  ounce  of  the  metals  or  cause  their 
dissolution  from  an  electrolytic  condition  with  the 
above  current  would  require  as  many  ampere-hours  as 
grains  deposited  by  one  ampere  is  contained  times 
into  480  grains.  We  can  facilitate  matters  by  in- 
crease of  amperes  of  current  up  to  a  certain  point, 


78  CYANIDE   PROCESSES. 

beyond  which  excess  of  quantity  does  not  precipitate 
faster,  but  injures  the  electrodes  and  electrolyte. 
Laboratory  tests  are  the  only  sure  criterion  for  the 
quantity  of  current  necessary,  but  these  tests  will  be 
founded  on  the  above  facts,  with  others,  which  are 
also  is  determined  in  the  laboratory. 

Knowing  the  quantity  of  solution  in  which  a  certain 
percentage  of  cyanide  of  potassium  is  placed,  and  then 
ascertaining  the  percentage  of  gold  in  that  solution,  we 
can  calculate  the  necessary  amount  of  current  to 
deposit  that  metal  uniformly.  Every  different  elec- 
trolyte must  be  electrolyzed  at  a  particular  rate  in 
order  to  continuously  obtain  from  it  the  desired  quan- 
tity of  metal. 

Increased  density  of  the  current  is  attended  by  in- 
creasecTTfeat  of  conduction  resistance  in  the  liquid, 
which  has  the  effect  of  dissolving  the  anode,  and  in 
our  case  nothing  more.  "It  is  not  by  misdirected 
strength  of  current,  however  great,  that  reducible  ele- 
ments are  separated."  From  a  weak  solution  of  a 
potassium  salt  even  the  strongest  current  will  not 
enable  us  to  obtain  the  metal ;  but  by  using  a  cathode 
of  mercury  of  small  surface  the  metal  has  been  de- 
posited by  the  aid  of  a  feeble  current.  It  thus 
becomes  evident  that  the  energy  must  be  intelligently 
directed. 

To  liberate  480  grs.  of  gold  it  would  require 
4.80  -f-  38.1  —  12.6  ampere-hours,  and  to  liberate 


CYANIDE  PROCESSES.  79 

480  grs.  of  potassium  cyanide  from  the  solution  would 
require  12.7  ampere-hours ;  but  in  our  solution,  follow- 
ing Eisner's  equation,  for  every  two  parts  of  gold 
liberated  we  must  liberate  two  parts  of  KCy  (potas- 
sium cyanide),  hence  the  number  of  ampere-hours 
would  be  12.7  X  2  =  25. 4  for  potassium  cyanide. 
Thus  to  liberate  one  ounce  of  gold  from  a  solution 
of  2K2AuCya  would  require  386  ampere-hours,  or  if 
the  work  was  to  be  performed  in  10  hrs.  3.86  amperes 
perhour  for  10  hours. 

By  using  more  amperes  we  of  course  waste  power, 
and  injure  the  electrolyte  for  future  use  by  oxygeniz- 
ing it  so  that  its  potassium  is  lost,  hence  free  hydro- 
cyanic acid  set  free. 


CHAPTER  XL 
CYANIDE  SOLUTION  WITH  VARIOUS  ELECTRODES. 

ELECTRO-GILDING  has  been  in  use  over  half  a 
century.  Dr.  Wright  of  Birmingham,  England,  used 
gold  cyanide  solution  for  electro-gilding  in  1840. 

The  principle  is  that  of  depositing  gold  from  a  gold 
solution  upon  a  cathode  of  metal  to  be  plated. 

The  current  or  circuit  is  made  so  that  electrical 
action  must  take  place  between  the  electrodes  through 
an  electrolytic  compound  of  liquid.  The  current  de- 
composes the  liquid  at  the  cathode,  giving  up  its  metal 
or  liberating  the  electrolyte  and  its  metal  constituent 
from  solution. 

Eisner's  equation  has  with  electrical  action  the  same 
features  as  it  possessed  where  cyanide  and  zinc  pre- 
cipitation were  employed.  The  oxygen  decomposes 
the  potassium  of  the  potassium  cyanide  as  before, 
except  more  briskly. 

In  this  instance  agitation  is  not  as  important  for 
generating  oxygen  as  it  is  for  moving  the  ore  and  liquid 
so  that  the  electrolyte  can  come  in  contact  with  the 
electrodes,  in  one  instance  receiving  life  for  dissolving, 
in  the  other  delivering  up  its  metal  and,  becoming  re- 
generated, and  sent  on  its  way  to  dissolve  more  gold. 

80 


CYANIDE  PROCESSES.  8 1 

By  electrical  action  the  cyanide  can  be  greatly 
reduced  in  the  liquor.  As  we  have  seen,  theoretically  I 
part  of  cyanide  solution  should  dissolve  1.5  parts  of 
gold,  but  that  practically  it  requires  48  to  64  times  that. 

By  the  aid  of  electricity  in  connection  with  cyanide 
the  amount  needed  has  been  reduced  to  16  parts  cya- 
nide to  i  part  gold,  and  we  are  of  the  opinion  it  will 
approach  nearer  the  theoretical  limit  as  matters  are 
improved.  As  the  solvent  action  takes  place  very 
much  quicker  for  some  cause,  and  as  there  is  not  the 
loss  of  cyanide  as  in  percolation  and  zinc-precipitation, 
a  very  great  saving  in  expense  and  time  is  recorded. 
Another  item  of  consideration  is  that  the  liquid  re- 
maining will  not  contain  the  impurities  deleterious  to 
future  action  in  anywhere  near  the  proportions  that 
it  must  in  the  former  process.  When  we  considered 
the  former  plan,  we  noticed  that  two  or  three  changes 
of  the  solution  were  practised,  with  intervals  between 
during  which  oxygen  was  allowed  to  act  upon  the  ore, 
to  furnish  the  necessary  electro-negative  element  to 
unite  the  cyanide  and  gold. 

By  the  use  of  electricity  the  electro-negative  ele- 
ment is  always  present  at  the  anode ;  this  allows  of 
the  operation  being  continued  without  loss  of  time  for 
percolation,  and  of  its  being  continued,  so  long  as  any 
potassium  cyanide  is  in  the  solution,  or  any  of  the 
precious  metals  to  be  dissolved.  We  have  stated  that 
agitation  with  the  current  passing  is  not  so  necessary 


82  CYANIDE  PROCESSES. 

as  in  the  former  practice,  nor  would  it  be  as  far  as 
oxidation  and  precipitation  go,  but  there  are  other 
considerations  which  make  it  desirable  that  the  sludge 
be  kept  in  motion. 

The  solution  is  very  weak,  and  in  order  to  hasten 
its  action  mechanical  power  should  be  used.  While 
it  is  possible,  that  by  liberation  of  gases,  and  the  ac- 
tion of  gravity  due  to  different  densities  of  the  elec- 
trolytes, either  with  or  without  gold  in  suspension 
would  create  circulation,  still  the  fact  is  that  the 
sludge  would  settle  around  and  on  one  or  more  of  the 
cathodes,  thus  hindering,  if  not  entirely  stopping  the 
deposition  of  the  metals  on  the  cathode.  Were  the 
liquid  clear  or  filtered  from  the  sludge,  this  would  not 
be  the  case,  but  by  filtering  we  lose  time  and  can 
not  perform,  neither  can  the  cyanide  do  the  work  as 
readily  as  it  is  accomplished  by  agitation. 

One  object  of  using  electricity  is  to  save  time, 
cyanide,  and  zinc ;  to  do  away  with  several  tedious  fil- 
terings or  percolations,  as  they  are  called ;  and  to  do 
what  leaching  is  required  with  one  solution,  at  one 
time  ;  and  precipitate  the  gold  at  the  same  time  that  the 
operation  is  carried  on  in  the  vat.  To  accomplish  this 
our  apparatus,  must  with  the  solution  satisfy  the  fol- 
lowing conditions :  There  must  be  a  metal  anode  not 
easily  corroded  or  dissolved  by  the  solution.  The 
proper  position  of  this  anode  is  above  the  cathode ; 
but  it  can  be  parallel  to  it  if  both  are  perpendicular. 


CYANIDE  PROCESSES.  83 

When  horizontal  and  in  courses,  the  oxides  from  the 
anode  fall  away,  and  being  deposited  on  the  cathode 
will  interfere  with  its  action,  especially  if  they  can  unite 
chemically  with  it.  Secondly,  the  cathode  must  allow 
the  gold  to  adhere  to  it,  and  after  the  process  is 
completed  allow  the  metal  to  be  easily  recovered. 
When  the  gold  must  be  dissolved  from  the  cathode 
by  acid,  such  sheets  of  thin  metal  as  can  be  readily 
removed  from  the  vat  should  be  used,  the  thin  gold 
can  then  be  removed  by  scraping  the  plates.  These 
plates  should  also  be  arranged  so  as  to  be  easily  lifted 
out  and  returned  to  the  vat,  or  if  mercury  is  used  it 
must  be  arranged  to  run  off  readily  so  that  it  can  be 
strained  and  returned  to  the  vat.  Each  inventor  has 
the  best  mode  of  accomplishing  these  results,  or  at 
least  did  have  until  some  one  else  overtopped  him. 

As  power  must  be  used  for  agitation,  it  must  be 
such  as  will  stir  up  the  whole  mass  and  keep  it  in 
motion.  It  occurs  to  us,  the  anode  being  the  dis- 
solving-point and  the  cathode  the  receiving-point, 
that  if  the  power  be  applied  to  either  one,  that  is,  the 
mechanical  power,  it  should  be  applied  to  the  anocle. 
If  we  can  apply  this  power  to  either  electrode,  we 
have  simplified  matters  one  step  more,  by  lessening 
mechanical  complications. 

As  in  the  former  process,  the  easiest  and  best  way 
of  recovering  the  precious  metals  is  in  the  form  of 
amalgam. 


84  CYANIDE  PROCESSES. 

The  objection  offered  by  Von  Gernet  to  a  mercury 
cathode  is  impracticability,  on  account  of  the  large 
amount  necessary  to  carry  on  the  operation.  While 
we  agree  to  this  as  far  as  the  large  amount  goes, 
we  must  disagree  with  him  on  its  being  impracticable, 
considering  it  also  economical  as  well  to  use  mercury 
for  cathodes.  Von  Gernet  says  that  ' '  sheets  of 
copper  coated  with  mercury  have  been  used  unsuc- 
cessfully, because  the  mercury,  owing  to  the  action 
of  the  current,  will  penetrate  the  copper,  forming 
a  dry  amalgam  which  does  not  adhere  to  the  plate." 
If  Mr.  Von  Gernet  will  try  to  get  that  dry  amalgam 
off  from  a  copper  plate,  he  will  find  that  it  does  not 
fall  off  readily,  and  will  not  penetrate  the  copper 
more  than  during  ordinary  copper-plate  amalgama- 
tion of  the  gold  mills,  but  it  gets  against  it  some  way 
decidedly  tighter. 

Of  course  the  mercury  will  become  dry  in  time,  in 
other  words,  will  wear  out ;  to  avoid  this  recover  the 
gold  once  in  a  while,  and  put  on  a  fresh  coat  of  mer- 
cury. The  cathode  of  lead  which  is  used  by  Sie- 
mens and  Halske  has  the  disadvantage  of  wearing 
out,  and  requires  to  be  as  thin  as  is  consistent  with 
mechanical  stability.  It  is  used,  however,  to  smelt 
the  gold  in  recovery  or  refining  of  the  deposit,  and  is 
a  very  long  way  ahead  of  zinc  recovery  in  that  re- 
spect. Siemens  and  Halske  thus  made  two  great  im- 
provements over  the  old  process,  viz.,  saving  of  cya- 


CYANIDE   PROCESSES.  85 

nide    and    zinc,    and    the    attendant    troubles    in    re- 
fining. 

It  is  not  in  our  province  to  criticise  any  one ;  we 
wish  to  ascertain  just  what  the  improvements  are 
which  tend  to  make  the  subject  more  applicable  to 
the  extraction  of  gold  from  ores,  and  to  point  out  de- 
fects as  we  see  them.  Should,  therefore,  an  amalga- 
mated copper  plate  be  placed  in  a  vat  with  the  amal- 
gam dry  on  it,  the  chances  for  its  being  scraped  off 
by  abrasion  or  grinding  of  the  ore  is  possible,  espe- 
cially if  the  mercury  be  small  in  amount  and  the  liquor 
circulating  strong.  The  electrical  current,  together 
with  the  adhesion  of  the  mercury  to  the  copper  plate, 
keep  the  gold  in  contact  with  the  plate.  If  too  much 
mercury  be  used,  it  will  be  forced  into  a  free  state, 
but  if  enough  is  used  to  keep  the  amalgam  plastic  and 
no  more,  it  will  not  be  rubbed  off.  However,  to  avoid 
such  chances  as  these  mercury  in  large  quantities  is 
poured  into  the  vat  to  act  as  a  cathode.  The  action  of 
the  liquid  in  circulating  may  give  this  liquid  mercury 
the  same  movement  as  its  own,  but  as  it  is  denser 
than  the  liquid  it  only  partially  assumes  the  motion. 
Still  it  is  sufficient,  where  horizontal  circular  motion 
is  employed  to  move  the  mercury,  to  at  times  uncover 
the  bottom  of  the  vat  in  places.  Just  at  this  point 
mercury  cathodes  fail,  for  the  molecule  wishing  to 
deposit  its  atom  of  gold  may  hit  a  bare  spot  and 
the  next  moment  be  lifted  awav.  To  overcome  this 


86  CYANIDE   PROCESSES. 

difficulty  a  copper  amalgamated  plate  can  be  used 
in  connection  with  the  mercury,  so  that  if  the  liquid 
mercury  is  disturbed  the  atom  of  gold  may  be  de- 
posited on  the  copper  plate.  Other  cathodes  besides 
mercury  and  lead  have  been  tried,  such  as  carbon, 
but  of  these  we  will  speak  in  another  chapter. 


CHAPTER  XII. 

THE  CURRENT. 

THE  quantity  and  the  energy  of  current  required  for 
the  electro-cyanide  process  of  dissolving  gold  and 
silver  from  their  ores  are  variously  stated. 

If  in  a  fixed  time  a  given  electric  current  will 
deposit  a  certain  quantity  of  metal,  as  we  are  told, 
it  will  be  in  direct  proportion  to  their  electro-chemical 
equivalents.  "This  law  holds  good  only  for  solu- 
tions strong  in  metal;  but  with  dilute  solutions,  as 
used  in  the  cyanide  process,  the  current  does  not  find 
sufficient  of  the  metallic  compound  present  at  the 
electrodes,  and  consequently  decomposition  of  the 
water  takes  place.  For  this  purpose  to  make  the 
efficiency  of  the  precipitation  as  great  as  possible 
constant  diffusion  of  the  solution  is  requisite." 
(Von  Gernet.) 

If  we  have  in  our  ore  one  ounce  (480  grains)  of  gold 
and  two  ounces  (960  grains)  of  silver,  and  we  wish  to 
precipitate  this  quantity  in  10  hours,  we  will  require 

•=1.2  amperes  of  current  for  gold, 


38.1  X  10 

87 


88  CYANIDE   PROCESSES. 

and 

060 

=  1.32  amperes  of  current  for  silver; 


but  we  have  the  potassium  as  well  to  liberate,  which 
for  gold  in  solution  will  be  theoretically  I  oz.  gold  = 
2  oz.  potassium  ;   hence 
960 


The  total  amperes  would  then  be  for  the  three  metals 
5.12  amperes  per  hour,  but  as  the  amperes  for  one 
are  sufficient  for  all  three,  the  highest,  5.12,  may  be 
considered  the  quantity  required.  Should  we  have 
one  hundred  tons  of  such  ore  to  be  treated,  our  volt- 
age must  be  considered.  Suppose  in  treatment  we 
used  one  half  horse-power  =  275  foot-pounds  per 
second  ;  as  I  watt  =  .7373  foot-pounds  per  second,  we 
would  use  372  watts,  but  a  watt  is  the  product  of 
amperes  by  volts,  hence  372-1-51.2  gives  the  voltage 
as  7.2. 

In  copper-refining  the  electrodes,  that  is,  the  anodes 
and  cathodes,  are  given  the  same  superficial  surface 
as  nearly  as  possible.  The  reason  for  this  is  to  afford 
as  much  dissolving-surface  as  plating-surface  that  the 
result  may  be  uniform.  In  our  instance  where  the 
anode  is  stationary  this  may  be  followed,  but  where 
the  movement  of  anode  relative  to  the  cathode 
takes  place  this  is  not  possible.  Again,  where  mer- 


CYANIDE   PROCESSES.  89 

cury  is  the  cathode,  it  is  well  to  have  it  as  small  as 
possible,  but  not  smaller  than  the  anode.  Von  Gernet 
says  ''that  a  better  effect  is  produced  by  doubling  the 
surface  of  electrodes  than  by  increasing  the  current 
tenfold."  He  was  speaking  of  the  Siemens-Halske 
precipitating-vat. 

The  iron  anodes  in  that  vat  or  series  of  vats  had 
14,000  square  feet  of  surface,  while  the  cathodes  had 
12,000  square  feet  of  surface  and  were  of  lead. 

The  current  of  electricity  used  was  from  a  5  H.P. 
engine,  and  yielded  3^  H.P.  in  electrical  energy  at  4 
volts  pressure. 

746  watts  X  3i  H.P. 

4  volts  =  652.75  a^res. 

Anodes  of  iron,  carbon  and  zinc  were  tried  ;  the  carbon 
could  not  stand  the  action  of  the  current  and  it  was 
abandoned  ;  while  zinc  formed  a  white  precipitate  and 
was  otherwise  objectionable.  Iron  was  finally  adopted, 
although  it  precipitated  Prussian  blue.  Iron  as  an 
anode  is  little  acted  upon  by  cyanide  of  potassium,  but 
if  the  electrolyte  is  overcharged  it  acts  upon  the  iron 
to  corrode  it.  Wrought  iron  is  more  readily  oxidized 
than  cast  iron  when  used  as  anodes.  It  requires  a 
definite  amount  of  current  to  oxidize  a  deh'nite  amount 
of  iron,  and  in  this  instance  1080  Ibs.  were  oxidized 
in  a  month ;  the  gold  percipitated  in  that  time  was 
335,935  grs.  in  700  hours,  or  4/09  grs.  per  hour. 


90  CYANIDE   PROCESSES. 

According  to  the  gold  ampere-hour  of  38.1  grs.,  it 
requires  8817  ampere-hours  to  deposit  this  amount. 
But  Butters  and  Smart  say  300  amperes  were  used, 
and  that  is  to  say  210,000  ampere-hours  were  ex- 
pended or  201,283  more  ampere-hours  were  ex- 
pended than  required.  The  current  necessary  to 
deposit  this  amount  of  gold  was  12.6  amperes. 

Hence   the   efficiency   of  the   current  —  -   =  4.2  per 

cent,  and  the  wasted  energy  was  expended  upon  the 
iron. 

As  we  stated  before,  the  electrodes  should  be  as 
nearly  of  a  size  as  possible  when  we  want  to  obtain 
equal  results.  They  should  be,  especially  the  anode, 
of  a  metal  or  substance  not  easily  acted  on  by  the  solu- 
tion ;  iron  seems  to  be  suitable  to  fulfil  the  conditions 
of  the  anode,  as  it  is  not  readily  acted  upon  by  the 
solution,  and  when  oxidized  it  is  due  in  great  measure 
to  having  the  current  too  energetic  for  the  work  in  hand. 

There  must  be  a  certain  amount  of  energy,  but  not 
too  much.  The  amount  should  be  determined,  as  we 
have  tried  to  show,  by  the  work  in  hand  to  be  per- 
formed. If  to-day  a  two-ounce  gold  ore  is  to  be 
treated  in  ten  hours,  more  amperes  will  be  required 
than  if  a  one-ounce  ore  were  to  be  treated  to-morrow 
in  the  same  time,  and  the  oxidation  of  the  anode 
will  not  be  more,  since  surplus  energy  has  not  been 
expended  upon  it. 


CYANIDE   PROCESSES.  9! 

The  question  of  the  size  of  anodes  and  cathodes, 
that  is,  the  surface  exposed  where  agitation  is  used, 
especially  iron  and  mercury,  is  purely  theoretical. 
The  anode  in  some  cases  is  not  more  than  one 
twentieth  the  surface  of  the  cathode,  and  yet  the  iron 
anode  is  not  very  materially  oxidized.  This  may 
be  due  to  the  movement  of  the  anode,  which  rotates 
horizontally  over  the  cathode  of  mercury,  but  at  some 
distance  from  it.  However,  it  does  not  seem  possible 
that  this  rotation  has  much  to  do  with  it,  since  the 
current  is  continuous,  and  the  voltmeters  and  ampere- 
meters do  not  show  any  variation  of  importance.  We 
would  suppose  that  energy  would  be  expended  more 
upon  this  anode,  but  we  must  take  the  facts  as  they  are. 

It  has  occurred  to  me  the  electrolyte  was  a  good 
conductor  of  the  current,  and  that  not  being  often  in 
contact  in  a  state  of  metalloid  with  the  cathodes,  con- 
ducted the  current,  which  was  proportioned  right  for 
the  work,  to  the  anode  and  cathode,  as  if  it  were  part 
of  a  circuit.  While  the  heat  arising  from  the  con- 
duction resistance  throughout  the  electrolyte  naturally 
reduces  the  resistance,  it  is  small,  and  that  leads  us 
again  to  think  that  potassium  cyanide  with  pulp  is  a 
good  conductor.  The  quantity  of  energy  lost  by  the 
corrosion  of  the  cathode  is  very  small,  as  the  mercury 
does  not  corrode  appreciably. 


CHAPTER   XIII. 
ANODES. 

THE  anode,  or  positive  pole,  is  the  one  by  which 
the  current  enters  the  solution,  and  it  is  at  this  pole 
that  the  dissolving  action  takes  place.  Anodes  not 
readily  corroded  by  chemical  action  resist  the  passage 
of  the  current.  For  instance,  an  iron  anode  in  a  solu- 
tion of  potassic  cyanide  requires  considerable  elec- 
tro-motive force  to  produce  electrolysis.  Little  gas  is 
evolved  at  the  anode,  and  it  is  not  corroded.  Should 
gas  evolve  at  the  anode,  the  current  passes  readily, 
and  the  anode  dissolves  rapidly.  With  an  anode  com- 
posed of  an  alloy,  the  most  easily  corroded  metal  is 
first  attacked.  At  times  the  anode  does  not  dissolve, 
and  becomes  coated  with  an  oxide,  which  hinders  the 
current,  but  that  anode  which  offers  the  least  resist- 
ance to  a  current  will  dissolve  most  readily. 

Usually  the  loss  of  the  anode  is  greater  than  the 
gain  of  the  cathode,  but  very  frequently  less  than 
theory  indicates,  because  while  chemical  action  is  tend- 
ing to  unite  the  constituents,  the  electrical  action  of 
the  current  is  trying  to  separate  them.  We  were  told 

that  when  a  non-corroded  substance  is  used  as  anode  an 

92 


CYANIDE   PROCESSES.  93 

elementary  substance  is  set  free  at  that  electrode,  but 
these  elementary  substances  set  free  may  unite  chem- 
ically with  other  substances  present  and  form  new 
compounds.  To  avoid  this  in  our  case  an  anode 
should  be  used  which  will  not  form  substances  detri- 
mental to  the  cyanide  solution  for  future  use. 

Let  us  now  consider  some  of  the  anodes  used  by 
the  various  inventors  in  their  researches  to  obtain  the 
gold  and  silver  from  ores  by  electrical  action  with 
cyanide  potassium  salts.  Julio  H.  Rea  (patent  1867) 
used  as  platinum  anode.  Platinum  as  an  anode  offers 
great  resistance  to  the  passage  of  an  electric  current ; 
if  silver  is  taken  as  i ,  platinum  offers  97  times  more 
resistance.  This  quality  is  objectionable  at  the  start, 
since  it  causes  heat,  and  offers  more  resistance  to  pas- 
sage of  current,  thus  decreasing  the  conductivity  of 
the  electrolyte.  It  also  takes,  on  account  of  resist- 
ance, more  time  or  more  electro-motive  force  to  deposit 
the  same  amount  of  metal  in  a  given  time.  Owing  to 
the  fact  that  decomposition  must  take  place  at  the 
anode  of  the  electrolyte,  energy  is  expended,  not  on  the 
work,  but  in  setting  free  oxygen  from  the  electrolyte, 
with  the  possibility  of  decomposing  it.  Another  ob- 
jection to  platinum  would  be  its  great  cost.  Still  in 
an  ampere-hour  the  amount  of  dissolution  of  platinum 
should  be,  since  it  is  a  tetrad,  28.62  grs.,  or  3/4  as 
much  as  gold.  There  do  not  seem  to  be  others 
than  Mr.  Rae  who  suggest  platinum  as  an  anode,  due, 


94  CYANIDE   PROCESSES. 

no  doubt,  to  its  cost,  which,  for  practical  work,  would 
be  exceedingly  large. 

Carbon  is  suggested  by  Malloy's  process,  1884  and 
1886.  In  this  case,  as  with  platinum,  oxygen  escapes. 
The  carbon  is,  however,  practically  unacted  upon  by 
the  anion  chemically,  but  the  current  or  the  oxygen 
mechanically  disintegrates  the  carbon.  The  greater 
the  current  the  more  rapid  the  disintegration. 

It  is  further  objectionable  because  of  energy  of 
current  lost,  and  possibly  the  active  energy  of  the 
electrolyte. 

Eissler  in  speaking  of  the  Halske-Siemens  process 
says :  "  Carbon  could  be  used  as  an  anode,  but  will  not 
stand  the  action  of  the  current,  and  soon  crumbles  into 
a  fine  powder  which  decomposes  cyanide."  "This 
finely  divided  carbon  is  in  suspension,  and  cannot  be 
removed  from  the  solution  by  filtration."  On  the 
other  hand,  Mr.  Weightman  used  arc-light  carbons  for 
six  months  and  they  were  still  in  good  condition. 
Mr.  Weightman's  observations  do  not  agree  with  Mr. 
Eissler's,  but  that  is  not  due  to  error  on  either  side. 
One  undoubtedly  had  reference  to  porous  carbons, 
while  the  other  had  reference  to  dense  compact  car- 
bons, coated  with  copper.  The  copper  coating  was 
of  very  great  assistance  even  to  the  compact  car- 
bon in  counteracting  disintegration  of  the  carbon 
by  the  current.  The  great  objection  to  carbon  is  its 
lack  of  conductivity;  if  silver  be  100,  then  carbon  as 


CYANIDE  PROCESSES.  95 

graphite  is  .069,  and  as  gas  coke  .038.  An  advantage 
in  its  use  is  its  small  power  of  dissolution,  which  is 
but  1.74  ampere-hours;  hence  it  could  cause  little 
deposition  without  great  electrical  energy. 

Cassel,  H.  R.,  used  carbon  rods  as  anodes,  as  did 
Fischer  and  Weber  (patents  1883,  1885,  and  1887). 
Mr.  J.  B.  Hanney  used  a  mixture  of  plumbago  and 
resin  as  anode,  and,  as  he  claims,  with  very  good  effect. 
As  a  rule,  the  anodes  have  been  varied  but  little,  but 
in  some  patents  they  have  had  different  arrangements, 
so  as  not  to  conflict. 

Zinc  as  anode  has  serious  defects,  in  fact  as  numer- 
ous as  when  used  as  a  cathode.  It  forms  a  precipitate 
of  cyanide  of  zinc  in  the  solution  ;  also  zinc  oxide  on  its 
surface,  which  offers  resistance  to  the  electro-motive 
force,  making  it  expensive.  Should  it  precipitate  on 
the  cathode,  it  will  also  cause  future  annoyance,  and 
as  one  of  the  advantages  claimed  for  electrolysis  is  that 
it  does  away  with  zinc  impurities,  should  we  consider 
zinc  at  all  in  connection  with  electricity,  we  have  gone 
backward  instead  of  forward  in  the  perfection  of  the 
system. 

Zinc  will  cause  the  solution  and  deposition  of  18.95 
grains  in  ampere-hour ;  hence  it  is  only  slightly  better 
than  iron  as  a  conductor,  while  very  much  inferior  as 
far  as  by-products  from  the  operation  are  concerned. 
Barker's  process,  1882,  had  for  anode  brass,  and  did 
not  use  cyanide  solution,  but  had  for  its  object  the 


96  CYANIDE  PROCESSES. 

preventing  of  mercury  from  sickening.  Leaving  out 
the  anode  and  substituting  cyanide  solution  for  water, 
we  believe  his  invention  would  be  successful  in  a  large 
degree;  otherwise  we  would  not  mention  it  here. 
The  subject  of  anodes  for  copper-refining  and  electro- 
plating is  well  known ;  the  conditions  of  such  anodes 
compared  with  anodes  for  the  electro-cyanide  process 
are  so  vastly  different  that  we  can  only  approach  them 
in  practice. 

For  copper-refining  the  anode  is  stationary,  and  the 
same  may  be  said  for  electro-plating  in  general,  but 
in  our  case  we  wish,  if  possible,  to  have  movable 
anodes,  which  do  mechanical  and  electrical  work  at  the 
same  time.  Again  the  ever-changing  classes  of  ore  as 
far  as  the  quantities  of  gold  and  silver  in  the  ore  are 
concerned,  make  the  matter  of  proportioning  the  size 
of  cathodes  very  difficult  to  meet  theoretical  require- 
ments. 


CHAPTER    XIV. 
CATHODES. 

THE  cathodes  next  require  our  attention,  and  these 
are  as  important  as  the  anodes,  and  possibly  more  so. 
Upon  these  the  metal  from  the  solution  is  to  be  de- 
posited, and  as  we  wish  to  obtain  that  metal  in  such 
form  as  to  refine  it  with  least  complications  and  skill, 
the  most  satisfactory  cathode  must  fulfil  conditions 
more  trying  than  the  anode.  It  is  the  pole  of  the 
current  from  which  the  current  passes  out  of  the 
liquid,  so  that  any  chemical  decomposition  or  disinte- 
gration of  the  molecules  of  the  electrolyte  must  take 
place  here.  It  must  be  a  good  conductor  of  electricity 
and  must  not  be  readily  corroded.  As  a  rule,  insoluble 
coatings  are  less  frequent  than  at  the  anode,  happen- 
ing generally  when  highly  oxidizable  metal  is  sepa- 
rated. A  film  of  hydrogen  sometimes  adheres  to  the 
cathode,  which  will  slightly  diminish  the  current. 

The  density  of  the  current  at  the  cathode  needs  to 
be  so  regulated  as  to  allow  the  metals  to  be  deposited 
as  metals,  and  not  as  powder,  and  as  we  are  dealing 
with  compound  substances,  the  cathode  should  be  of 
such  a  nature  as  not  to  unite  readily  with  the  second- 
ary products  of  electrolysis.  From  an  impure  solution 

97 


98  CYANIDE  PROCESSES. 

the  least  electro-positive  metal  should  be  deposited 
upon  the  cathode  first;  consequently  with  our  solution 
containing  gold  and  potassium  cyanide,  silver  and 
potassium  cyanide,  as  double  salts  of  cyanide,  the  rate 
of  deposition  would  be  silver,  gold,  potassium ;  but  it 
is  doubtful  under  these  conditions  whether  it  is  neces- 
sary to  use  current  more  than  sufficient  to  liberate  the 
gold  and  silver,  allowing  the  KCy  to  remain  in  solu- 
tion undisturbed.  If  this  can  be  accomplished,  there 
will  be  considerable  voltage  saved  as  well  as  cyanogen. 
Unable  to  obtain  any  reliable  information  regarding 
electrolysis  of  mixed  solutions,  we  can  only  draw  con- 
clusions from  observations.  We  know,  however,  that 
the  current  will  pass  through  an  electrolyte  when 
feeble  so  as  not  to  cause  electrolysis,  and  that  aqueous 
solutions  of  the  zinc  and  copper  cyanides  will  dissolve 
and  deposit  equally  on  passage  of  suitable  current ;  so 
we  are  led  to  infer  from  these  phenomena,  since  the 
electro-motive  forces  of  zinc  and  copper  are  equal,  that 
the  least  abundant  metal  will  deposit  least ;  but  if 
equally  solvent  in  the  solution  the  least  electro-posi- 
tive will  deposit  first,  and  this  latter  has  been  proven 
in  the  case  of  silver  salt  in  copper  solution.  The  size 
of  the  cathode  should  be  larger  than  the  anode  if  its 
conductivity  is  less,  but  may  be  smaller  on  the  reverse 
of  this  proposition.  It  should  be  of  sufficient  size, 
however,  to  be  able  to  absorb  or  receive  as  much 
metal  as  is  offered  for  deposition. 


CYANIDE  PROCESSES.  99 

If  the  vat  is  used  with  agitation,  the  cathode  should 
be  as  large  as  the  diameter  of  the  vat,  so  that  every 
chance  for  deposition  be  accorded  the  solution,  and  not 
be  contracted  by  a  small  cathode,  which  must  focus 
the  current  from  the  electrolyte. 

Julio  Rea  used  copper  cathode  without  amalgamat- 
ing it ;  Mr.  Simpson  used  a  zinc  cathode  ;  Michel  Body 
(patent  1894)  uses  mercury  in  a  contrivance;  Mr. 
Hanney  used  mercury;  Mr.  Whitall  an  iron  cathode; 
Chas.  Raleigh  employed  copper  saturated  with  mer- 
cury; Mr.  Keith  uses  copper  plates  preliminarily 
treated  with  mercury  ;  Siemens-Halske  use  thin  sheets 
of  lead  ;  Barker  used  mercury,  as  stated ;  Fisher  and 
Weber  mercury  and  metal  plates. 

The  employment  of  mercury  seems  to  be  the  more 
general  for  cathodes  than  any  other  metal  except 
amalgamated  copper  plates.  Copper  makes  a  good 
cathode,  but  as  the  precious  metals  are  deposited 
upon  its  surface  dry  and  hard,  there  are  objections 
to  its  use  without  amalgam.  The  copper  plate  is 
very  little  wasted  by  the  current.  Mr.  Simpson's  zinc 
cathode  is  objectionable  for  reasons  stated.  Mr. 
Whitall's  iron  cathode  was  objectionable  because  the 
precious  metals  were  deposited  as  powder,  hence  no 
agitation  could  be  used ;  and  is  here  further  objec- 
tionable where  electricity  is  concerned  on  account  of 
impurities  in  the  bullion. 

Chas.  Raleigh  uses  mercury,  but  his  plan  of  pump- 


100  CYANIDE  PROCESSES. 

ing  mercury  through  between  two  active  surfaces,  as 
he  says,  makes  the  matter  dense.  (See  English 
patent  14,910,  1893.) 

Mr.  Keith's  mercury  and  copper  plates  will  answer 
admirably,  but  he  follows  on  the  lines  of  Siemens- 
Halske,  with  the  bad  plan  of  using  porous  cells,  and 
circulating  the  solution  after  leaching  through  boxes 
for  precipitation.  However,  it  does  away  with  zinc 
becoming  mixed  with  the  precipitate. 

Lead  cathodes  used  by  Siemens-Halske  are  very 
thin  sheets  of  lead,  and  to  obtain  the  gold  from  them 
they  are  smelted  with  the  gold.  The  process  has 
worked  very  successfully,  but  requires  smelting  skill. 

Pelatan-Clerici  process  uses  both  an  amalgamated 
plate  and  mercury;  also  carbon  cathodes  electrically 
copper-plated,  then  coated  with  mercury. 

There  are  other  processes  which  have  peculiarities 
which  we  will  touch  upon  in  general,  using  the  pat- 
entees' words,  for  we  have  had  no  chance  to  prove 
their  claims.  There  are  other  electrical  processes  for 
different  solutions  than  cyanide,  which  we  do  not 
attempt  to  follow. 

Wm.  Crookes  (patent  No.  462,535,  1891). 

He  says:  "  In  carrying  out  my  combined  process  I 
take  the  gold  ore,  tailings,  etc.,  and  mix  with  them  a 
solution  of  nitrate  or  cyanide  of  mercury,  and  pass  a 
rapidly  alternating  current  of  electricity  through  the 
mass,  either  when  at  rest  or  agitated  in  any  manner." 


CYANIDE  PROCESSES.  IOI 

"  The  bulk  of  the  mass  is  not  a  good  conductor  of 
electricity,  while  the  fine  particles  of  gold  are  excel- 
lent conductors."  "  Iron  or  carbon  can  be  used  as 
electrodes,  and  each  electrode  is  alternately  anode  and 
cathode."  "  Assuming  that  sulphate  of  mercury  is  the 
mercurial  salt,  the  current  liberates  sulphuric  acid  at 
one  pole  and  mercury  at  the  other. "  "  The  action  now 
being  reversed,  the  mercury  liberated  previously  has  a 
molecule  of  acid  to  unite  with  it,  so  that  at  each  pole 
the  mercurial  salt  is  decomposed  only  to  unite  again." 
Since  the  gold  in  the  wet  mass  is  a  better  conductor 
than  the  surrounding  mass,  the  equipotential  lines  of 
force  will  converge  toward  them,  so  that  more  of  the 
current  passes  through  them  than  the  rest  of  the 
mass,  and  the  two  sides  of  each  particle  of  gold  act 
as  anode  and  cathode.  On  one  side  sulphuric  acid  is 
liberated,  on  the  other  mercury,  but  the  arHnity  of 
gold  for  mercury  is  so  great  they  instantly  amal- 
gamate on  one  side,  finally  on  the  other  side.  Thus 
the  size  of  the  particles  is  not  essential,  as  the  finest 
flour  and  float  gold  will  be  amalgamated.  Nor  does 
it  matter  to  what  degree  of  coarseness  the  ore  is 
crushed  so  long  as  the  mercurial  salt  penetrates  to 
one  part  of  the  piece  of  gold  locked  up  in  the  ore,  for 
the  action  will  then  take  place  and  the  metal  become 
amalgamated." 

"The  advantage  incidental  to  the  use  of  an  alter- 
nating current  is  that  the  sudden  and  violent  deconv 


IO2  CYANIDE  PROCESSES. 

positions  and  recompositions  cause  the  mass  to  become 
hot,  and  so  greatly  facilitate  the  amalgamation." 

"The  efficient  action  is  dependent  upon  several 
variable  factors,  viz.,  current  density,  area  of  elec- 
trodes, rate  of  alternation  per  second,  and  electric 
conductivity  of  the  crushed  ore  and  liquid." 

We  are  not  aware  that  this  process  has  had  practi- 
cal application.  It  may  be  successful  in  the  laboratory 
on  rich  ores,  but  we  have  never  heard  of  it  beyond 
the  patent  specification.  We  have  quoted  it  because 
cyanide  can  be  used  in  connection  with  it,  and  it  is 
one  process  which  uses  the  alternating  current. 


CHAPTER    XV. 
VARIOUS   PROCESSES   AND  CONCLUSIONS. 

MR.  MAcARTHUR  said  that  when  cyanide  is  used 
in  combination  with  electric  current  not  only  is  there 
a  larger  expenditure  of  chemicals,  but  the  base  metals 
are  dissolved  to  a  large  extent  along  with  the  gold 
and  silver,  and  for  subsequent  separation  involve  extra 
expense,  which  is  saved  by  our  process. 

We  believe  he  was  afraid  of  the  Siemens-Halske 
process  at  the  time  he  said  that.  However,  we  must 
take  him  at  his  word. 

Mr.  Hanney,  a  countryman  of  his,  says  that  when 
the  electric  current  is  used  the  cyanide  solution  may 
be  weaker,  as  its  action  is  increased  by  the  current. 
He  further  states  that  only  metal  and  silver  salts  are 
attacked  by  the  solution,  and  that  copper  and  iron 
pyrites  may  be  stripped  of  their  gold  and  not  be  at- 
tacked otherwise. 

He  uses  mercury  for  a  cathode  and  obtains  the  gold 
direct  from  the  ore,  which  is  the  easiest  method  of 
collecting  it  for  subsequent  separation.  Another  ad- 
vantage he  obtains  in  this  collecting  of  the  precious 
metals  is  that  no  previous  treatment,  such  as  amalga- 
mation, is  required  for  the  coarser  particles  of  gold. 

103 


IO4  CYANIDE  PROCESSES. 

The  advantages  claimed  by  Mr.  Hanney  are  so 
broad  that  they  almost  amount  to  his  having  an  ideal 
apparatus. 

They  are :  That  the  precious  metals  are  extracted 
direct  from  the  ore. 

That  economy  is  practised  in  the  use  of  cyanide  for 
extraction,  thus  approaching  more  theoretically  to 
the  quantity  of  cyanide  necessary  for  the  dissolving  of 
gold. 

That  the  precipitated  metals  are  at  once  obtained 
from  the  amalgam  in  the  metallic  state,  thus  requiring 
no  chemical  or  intricate  treatment  after  precipitation. 

That  any  workable  quantity  may  be  treated,  so  as 
to  dissolve  and  precipitate  the  precious  metal,  and  re- 
cover the  bullion  in  one  day. 

That  when  the  process  is  completed  the  liquid  from 
the  tank  may  be  run  off  through  a  rough  filter  to 
clear  the  liquid  of  sludge  so  that  it  may  be  used  over 
again  by  being  brought  up  to  its  standard  for  re- 
covery. 

Percentages  recovered  from  three  different  ores  by 
this  process  gave  76.2,  86.9,  95.3,  an  average  of  86.1 
per  cent. 

He  further  hastened  the  solvent  action  of  the  cya- 
nide solution  by  agitating  the  solution  by  means  of 
a  screw  propeller  placed  in  the  bottom  of  the  vessel, 
which  gave  the  liquor  an  upward  movement  along  the 
sides,  then  down  through  the  centre  of  the  vessel  so 


CYANIDE  PROCESSES.  10$ 

as  to  come  in  contact  with  his  anode  of  plumbago  and 
resin. 

His  planning  to  obtain  all  the  good  points  was  ad- 
mirable. Rae's  was  not  quite  as  good,  and  Mr. 
Simpson  did  not  apparently  try  to  improve  or  push 
his  invention.  Siemens  and  Halske,  and  Dr.  Keith's 
inventions  were  only  broad  enough  to  deposit  the 
metals  after  percolation  to  avoid  the  trouble  incident 
to  zinc  precipitation,  and  what  advantage  Dr.  Keith 
gained  by  amalgamated  copper  plates  he  lost  by  using 
anodes  in  porous  cups  I  inch  diameter,  24  inches 
long,  the  cost  of  which  would  in  all  probability  equal 
the  cost  of  the  lead  by  Siemens-Halske's  process. 

The  most  recent  process  before  the  public  is  the 
Pelatan-Clerici.  They  put  forward  the  same  claims 
as  does  Hanney ;  they  say  that  while  the  simple  cya- 
nide process  is  not  capable  of  universal  application, 
their  process  is  more  applicable. 

That  where  the  recovery  of  gold  by  amalgamation 
is  from  55  to  60  per  cent  they  are  able  to  recover  85 
per  cent,  and  more.  They  say  that  under  the  most 
favorable  conditions  the  common  cyanide  process 
saves  68  per  cent  of  the  gold,  and  barely  50  per  cent 
of  the  silver. 

Their  claims  are  that  they  use  a  more  efficient  so- 
lution and  entirely  different  method  of  treating  the 
ore. 

The  treatment  consists  of  a  single  operation  which 


106  CYANIDE   PROCESSES, 

is  carried  on  in  a  vat.  This  vat,  in  the  centre  of 
which  is  a  stirrer  of  metal  (iron)  and  which  is  com- 
posed at  the  bottom  of  special  amalgamated  copper 
plates,  is  filled  with  crushed  ore  or  tailings. 

At  the  same  time  a  diluted  solution  containing 
cyanide  of  potassium,  common  salt,  and  some  other 
chemical  is  added,  the  portion  of  each  reagent  being 
calculated  according  to  the  quality  of  the  material 
treated. 

The  stirrer  is  then  set  in  motion  so  as  to  mix  the 
ore  with  the  solution,  and  to  make  a  liquid  sludge 
through  which  an  electric  current  generated  from  a 
dynamo  is  allowed  to  pass  freely.  The  particles  of 
precious  metals  are  thus  brought  again  and  again  into 
contact  with  quantities  of  cyanide  much  more  than 
sufficient  to  dissolve  them  entirely. 

Owing  to  the  very  efficient  dissolving  power  of  the 
solution  on  the  one  hand,  and  to  the  action  of  the 
electric  current  on  the  other  hand,  the  fine  gold  and 
silver  are  readily  dissolved,  and  afterwards  electrically 
deposited  on  the  amalgamated  plates  in  the  vat, 
where  they  can  be  recovered  in  the  form  of  amalgam. 

The  coarse  grains  are  amalgamated,  so  that  they 
are  also  recovered. 

This  process  admits  of  a  far  smaller  quantity  of 
cyanide  being  used  than  in  any  leaching  process 
known. 

The  time  required  for  working  a  charge  is  from  six 


CYANIDE  PROCESSES.  IO/ 

to  twelve  hours,  while  by  the  ordinary  method  as 
many  days  may  be  consumed — under  the  most  favor- 
able conditions  three  days. 

This  process  avoids  all  the  difficulties  and  complica- 
tions connected  with  the  leaching  and  washing  of  the 
tailings,  the  recovery  of  gold  and  silver  in  solutions, 
and  the  presence  of  baser  metals.  The  liquor,  i.e., 
solution  and  ore,  is  run  out  through  an  opening  in  the 
bottom  of  the  vat,  and  the  vat  is  then  ready  for  an- 
other charge  of  ore.  The  waste  liquor  is  allowed  to 
settle  in  a  tank  below  the  vat,  and  after  a  time  two 
thirds  of  it  are  drawn  off  to  be  used  again.  The  liquor 
contains  from  .001  to  .002  per  cent  of  cyanide  ;  it  holds 
in  the  solution  but  faint  traces  of  the  base  metals. 

This  process  is  said  to  work  better  with  slimes  than 
coarser  ore. 

The  cost  of  crushing  must  be  added  to  the  cost  of 
treatment  of  ore,  but  as  this  varies  from  50  cents  to 
$2.50  per  ton,  depending  upon  circumstances,  they  do 
not  consider  it  in  making  up  the  cost  of  the  process. 
This  crushing  cost  must  not  be  considered  in  compar- 
ing the  cost  with  tailings  treatment  which  is  the 
result  of  other  treatment,  unless  the  cost  of  crushing, 
amalgamating,  and  tailings  treatment  be  combined, 
since  those  operations  by  the  ordinary  processes  only 
accomplish  as  much  as  this  one  process. 

The  chemicals  used  are  2  to  3  Ibs.  potassium  cya- 
nide per  ton  of  ore  or  o.ooi  to  0.0015  per  cent  solu- 


108  CYANIDE  PROCESSES. 

tion ;  besides  sodium  oxide  (Na2O)  as  an  oxidizing 
agent,  or  lime.  This  reagent  is  not  given,  but  its  cost 
is  placed  at  50  cents  per  Ib.  As  cyanide  potassium  is 
50  cents  per  Ib.  and  two  thirds  are  recovered,  the 
total  cost  of  chemicals  is  $i  ;  labor  and  general  ex- 
penses are  placed  at  80  cents  per  ton,  10  per  cent 
interest  and  depreciation  on  plant  placed  at  20  cents 
per  ton.  Total  cost  of  treatment  $2  per  ton.  The 
capabilities  of  this  process  are  as  wide  as  by  the  older 
system,  with  the  advantage  of  recovery  of  more  silver. 
Conclusions  applying  to  both  methods,  simple  and 
electrical : 

1.  The  plant    required   is   comparatively   inexpen- 
sive. 

2.  The  extraction  is  arrived  at  without  any  previous 
treatment  of   ores,   except  ordinary    crushing,   which 
must  take  place  for  every  treatment. 

3.  The  extraction  is  simple,  and  quite  complete; 
tailings  can  be  treated  successfully  when  failure  has 
attended,  other  processes. 

4.  The  precious  metals  can  be  precipitated  from  the 
solution  in  various  ways  to  suit  the  ideas  of  the  oper- 
ator, but  the  simplest  way  is  by  the  electrical  current 
with  mercury  cathode. 

5.  The  simple  cyanide  process  extracts  only  the  fine 
gold,  thus  necessitating  previous  amalgamation  with 
free-milling,  and  longer  contact  with  the  solution,  and 
very  fine  crushing  with  refractory  ore.     The  electrical 


CYANIDE  PROCESSES.  1 09 

method  with  mercury  requires  no  previous  amalgama- 
tion. 

6.  The  cost  of  treatment  is  not  so  high  as  to  deter 
the  use  of  either  process,  and  at  times  is  quite  reason- 
able, depending  upon  circumstances. 

7.  The    factor   time   enters   into  competition   with 
machinery  on  the  one  hand,  while  machinery  enters 
into  competition  with  time  on  the  other.     We  have 
neglected  previously  to  state  an  important  factor  in 
favor  of  agitation,  viz.,  that  the  tanks  can  be  cleared 
more  readily  for  another  operation ;   with  percolation 
they  must  be  shovelled  out. 

8.  Talcose  and  clayey  ores,  such  as  make  leaching 
difficult  even  when  mixed  with  sand,  are  readily  treated 
by  agitation  and  the  electric  process. 

9.  Failure  to  obtain  satisfactory  results  has  occurred 
from  neglect  on  the  part  of  the  operator  to  properly 
oxidize    the   ore    before    applying  the    cyanide   solu- 
tion. 

Failure  has  occurred  in  other  instances  because 
sufficient  knowledge  of  the  process  was  not  possessed 
by  the  operator.  Early  experiments  proved  very 
unsatisfactory  especially  in  the  South  Atlantic  States, 
where  this  process  seems  to  have  been  tested  before 
it  had  attained  its  present  state  of  perfection,  or  rather 
before  the  intelligence  now  possessed  upon  the  subject 
had  been  acquired  by  experiment. 

Since   the  early  experiments  were  inaugurated  the 


110  CYANIDE  PROCESSES. 

process  has  gradually  obtained  prominence,  not  so 
much  from  writings  as  from  actual  results,  until  now 
we  have  come  to  realize  its  usefulness  in  the  treatment 
of  ores  which  we  considered  formerly  of  trifling  value, 
and  in  some  instances  of  no  value  whatever.  When- 
ever failures  are  to  be  recorded  in  the  future  of  this 
process,  they  will  be  due  to  the  following:  first,  at- 
tempting to  work  ores  not  suitable  for  the  cyanide 
process ;  and  secondly,  to  the  ignorance  of  the  op- 
erator. Those  who  intend  to  erect  extraction  works 
in  this  enlightened  age  of  mining  should  acquaint 
themselves  with  the  process,  and  ascertain  if  it  be 
applicable  to  the  ores  they  propose  to  treat.  It  is  not 
a  difficult  matter  now  to  ascertain  the  fitness  of  ore 
for  cyanide  treatment,  and  after  it  has  once  been  de- 
termined to  be  suitable  for  cyanide  treatment,  nothing 
but  an  absolute  change  in  the  character  of  the  ore  will 
interfere  with  its  successful  work,  except,  of  course, 
the  ignorance  of  the  operator. 

Mr.  F.  A.  Moson's  experiment  shows  that  where 
tailings  from  amalgamating  mills  are  treated,  and  the 
gold  particles  are  coated  with  mercury,  cyanide  will  not 
act  upon  them ;  this  will  account  in  some  measure  for 
not  obtaining  at  times  a  higher  percentage  of  extrac- 
tion with  the  older  cyanide  method.  This  objection 
is  removed  by  electrical  cyanide  process. 

In  the  treatment  of  concentrates  care  must  be  used 
to  have  them  finely  pulverized  for  cyanide  treatment 


CYANIDE   PROCESSES.  Ill 

when  they  do  not  yield  their  gold  readily  by  laboratory 
test. 

The  writer  is  indebted  to  the  following  people  and 
publications  for  information  and  data  (patents  U.  S. 
unless  otherwise  stated)  : 

Julio  H.  Rae  .......    No.    61,866,  Feb.  5,  1867 

Thos.  C.  Clark  .....    No.  229,586,  July  6,  1880 

H.  W.  Faucett  .....    No.  236,424,  Jan.  u,  1881 

J.  F.  Sanders  ......    No.  244,080,  July  12,  1881 

J.  W.   Simpson  .....    No.  323,222,  July  28,  1885 

MacArthur-Forrest.    No.  403,202,  May  14,  1889 

No.  418,138,  De4|.24,  1889 

No.  418,137, 

E.  D.  Kendall.    ...    No.  482,577,  Sept.  13,  1892 
B.  C.  Malloy  .......    No.     15,206,  Nov.  22,  1886 

July  8 


Carl  Moldehauer. 


J.  C.  Montgomerie  (English)..    . 

j  July  22,  1893 

Jan.  2,  1894 

July   I0>    l894 

Oct.  4,  1894 
Jan.  8,  1895 
Carl  Pielstecker.  ..................  Dec.,  1894 

Alexis  Janin     ) 

r    MT    iv/r      -11  f  •"•    No'  515,148,  Feb.  20,  1894 
C.  W.  Merrill  J 

W.  D.  Johnston  ____    No.  522,260,  July  3,  1894 
Pelatan  and  Clerici  ..............  Oct.  1  894 


112  CYANIDE  PROCESSES. 

Wm.  Crookes  (Eng.).  No.  462,535,  Nov.  3,   1891 

Siemens-Halske   Extracts 

J.  B.  Hannay 

S.  R.  Whitall April  18,  1893 

Chas.  Raleigh Extracts 

Michel  Body   Jan.  8,  1 894 

Carl  Hoepfner Oct.  24,  1 893 

Baker's  Process June  28,  1882 

C.  D.   Able Jan.  20,  1887 

W.  A.  G.  Birkin Mar.  21,  1893 

W.  P.  Miller Feb.  6,  1894 

Frederick  Rinder June  18,  1895 

-*-**/ 333. 

PUBLICATIONS. 

Engineering  and  Mining  Journal,  N.  Y.  City,  Dec. 
29,  1888. 

Mining  and  Scientific  Press,  San  Francisco,  Cal. 

Mining  Journal,  Railway  and  Commercial  Gazette, 
London. 

The  Mining  Journal,  London. 

California  State  Mining  Bureau. 

Journal  of  Electrical  Engineers. 

The  various  writers  whose  names  appear  have 
written  for  the  above  publications,  and  to  those  in- 
terested are  probably  well  known. 


C  YA  NID E  PRO  CESSES.  I  1 3 

USEFUL  INFORMATION. 

Area  of  circle  =  diameter  squared  X  .7854. 

Circumference  of  circle  =  diameter  X   3.1416. 
Cubic  inches  in  gallon  imperial  =  277.276. 

11     U.  S.       =  231. 
"   foot  =  1728. 

Cubic  foot   =      6.232  gallons. 
Cubic  yard  =  168.264        " 
Imperial  gallon  weighs  10  pounds. 
U.  S.  "  "          8.33  pounds. 

One  ton  water  =  200  imp.     gallons. 

"       "       "      —  240  U.  S.        " 
One  cubic  foot  water  weighs  62.5  pounds. 
Drachm  avoirdupois     —       27.3  grains. 

"  fluid  water  =  54.7  " 
One  cubic  inch  water  =  252.5  " 
Pennyweight  Troy  =24  " 
Ounce  avoirdupois  =  437.5  " 

11       Troy  =480 

Pound      "  =  5760          " 

*'       avoirdupois        =  7000          " 
Gram  =       15.432  " 

Grain  .0648  gram. 

Ounce  =      28.3495      " 

i  coulomb  =  unit  of  quantity  of  electric  current, 

i  ampere  —    "     *'  flow  =  I  coulomb  per  sec. 

i  ohm  =    "     "  conduction  resistance. 

i  volt  =    "     "  electro-motive  force. 

Assay  ton  =  450  grains  Troy  weight. 

"       *'  =  29, 1 66  milligrams. 

Avoirdupois  ton  =  2000  pounds  or  32,000  ounces. 
*'  "     =  29, 1 66  Troy  ounces. 


INDEX. 


Acid  ores,  54 

Agitation,  15,  29,  82 

Alkali  precipitation,  34,  60 

Alkaline  sulphides,  25 

Alternating  currents,  100 

Aluminum  precipitation,  36 

Amalgamation,  7 

Anodes,  92 

Bullion,  treatment  of,  43 

Ca*    ~>des,  97 

C)        oal  precipitation,  35 

ical  treatment  of  ores,  21 
'c    .entrates,  66 
rooke's  process,  100 
-ushing  ores,  3 
arrent,  72,  82 

"         and  cyanide  solution,  87 
yanide  and  stamp  battery,  5 
"       process,  10 
"          "     recovery,  48 
^termination  of  gold  and  silver,  54,  56 
"  "   ores,  22,  29,  49 

"  "   solution,  14,  56 

"   zinc  by  alkaline  sulphides,  60 
"  "      "      "  iodine,  58 

41  "      "     in  solution,  60 

lute  solutions,  14,  20 
•ainage  of  ore,  4,  17 
ectrodes,  80 
lectro-gilding,  80 
Jectrolysis,  73 
Eisner's  equation,  10 

US 


1 16  INDEX. 

Experiments,  n 
General  information,  63 
Gold  recovery  by  zinc,  33,  38,  51 
"  "          "    electrolysis,  78 

"     refining,  45 
Hanney  process,  12 
Laboratory-work,  54 
Leaching,  32 
Lime  treatment,  5 
Literature,  in 
Mercury  cathodes,  98,  105 
"         flouring  of,  8, 
"         sickening  of,  9 
Ores,  i,  7 

"      drainage,  4,  I7>  32 
"      for  cyanide  process,  17,  29,  50 
"      leaching  of,  29,  32 
"      refractory,  7 
"       tailings,  18,  31 
Paul's  rule,  15 

Precipitation  by  alkali,  34,  60 
"  "    aluminum,  36 

"  "    charcoal,  35 

"  "    Peletan-Clerici  method,  105 

"  "    Siemens-Halske  method,  99 

"  "    zinc,  33,  38 

Process,  10,  30 

"         chemistry  of,  21 
"         ores  adapted  to,  17,  29,  50 
"         recovery  by,  48 
"         scope  of,  22 
Sampling,  67 

Siemens-Halske  process,  99 
Solution,  14,  56,  87 
Stamp-milling,  2 
Useful  information,  113 


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